Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Mar. 14, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	CPRX
Entity Registrant Name	CATALYST PHARMACEUTICALS, INC.
Entity Central Index Key	0001369568
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		102,739,257
Entity Public Float			$ 298,397,093

Consolidated Balance Sheets - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 16,559,400	$ 57,496,702
Short-term investments	36,922,213	26,516,711
Inventory	56,012	0
Prepaid expenses and other current assets	1,649,781	1,173,744
Total current assets	55,187,406	85,187,157
Investments	5,008,243	0
Property and equipment, net	245,425	191,385
Deposits	8,888	8,888
Total assets	60,449,962	85,387,430
Current Liabilities:
Accounts payable	2,337,367	1,945,575
Accrued expenses and other liabilities	7,173,987	2,320,587
Total current liabilities	9,511,354	4,266,162
Accrued expenses and other liabilities, non-current	154,799	157,456
Total liabilities	9,666,153	4,423,618
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized: none issued and outstanding at December 31, 2018 and 2017	0	0
Common stock, $0.001 par value, 150,000,000 shares authorized; 102,739,257 shares and 102,549,498 shares issued and outstanding at December 31, 2018 and 2017, respectively	102,739	102,549
Additional paid-in capital	211,265,279	207,421,710
Accumulated deficit	(160,563,961)	(126,560,447)
Accumulated other comprehensive loss	(20,248)
Total stockholders' equity	50,783,809	80,963,812
Total liabilities and stockholders' equity	$ 60,449,962	$ 85,387,430

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	102,739,257	102,549,498
Common stock, shares outstanding	102,739,257	102,549,498

Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenues from collaborative arrangement	$ 500,000	$ 0
Operating costs and expenses:
Research and development	19,919,204	11,375,237
General and administrative	15,875,961	7,304,399
Total operating costs and expenses	35,795,165	18,679,636
Loss from operations	(35,295,165)	(18,679,636)
Other income, net	1,291,651	454,163
Change in fair value of warrants liability		(186,904)
Loss before income taxes	(34,003,514)	(18,412,377)
Provision for income taxes	0	0
Net loss	$ (34,003,514)	$ (18,412,377)
Net loss per share - basic and diluted	$ (0.33)	$ (0.21)
Weighted average shares outstanding - basic and diluted	102,633,884	85,802,487
Net loss	$ (34,003,514)	$ (18,412,377)
Other comprehensive loss:
Unrealized gain (loss) on available-for-sale securities	(20,248)
Comprehensive loss	$ (34,023,762)	$ (18,412,377)

Consolidated Statements of Changes in Stockholders' Equity - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2016	$ 39,308,930	$ 82,972	$ 147,374,028	$ (108,148,070)
Issuance of common stock, net	53,772,560	16,455	53,756,105
Issuance of stock options for services	2,342,625		2,342,625
Amortization of restricted stock for services	65,336		65,336
Exercise of warrants for common stock	3,518,553	2,258	3,516,295
Exercise of stock options for common stock	368,185	864	367,321
Net loss	(18,412,377)			(18,412,377)
Ending Balance at Dec. 31, 2017	80,963,812	102,549	207,421,710	(126,560,447)
Issuance of common stock, net	10,549	3	10,546
Issuance of stock options for services	3,535,647		3,535,647
Exercise of stock options for common stock	297,563	187	297,376
Other comprehensive loss	(20,248)				$ (20,248)
Net loss	(34,003,514)			(34,003,514)
Ending Balance at Dec. 31, 2018	$ 50,783,809	$ 102,739	$ 211,265,279	$ (160,563,961)	$ (20,248)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net loss	$ (34,003,514)	$ (18,412,377)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	37,978	45,689
Stock-based compensation	3,550,644	2,407,961
Change in fair value of warrants liability		186,904
(Increase) decrease in:
Inventory	(56,012)
Prepaid expenses and other current assets and deposits	(476,037)	(125,800)
Increase (decrease) in:
Accounts payable	391,792	1,012,399
Accrued expenses and other liabilities	4,850,743	1,142,652
Net cash used in operating activities	(25,704,406)	(13,742,572)
Investing Activities:
Purchases of property and equipment	(92,018)
Purchases of investments	(36,802,418)	(3,958)
Proceeds from maturities of investments	21,368,425
Net cash provided by (used in) investing activities	(15,526,011)	(3,958)
Financing Activities:
Proceeds from issuance of common stock, net		53,772,560
Payment of employee withholding tax related to stock-based compensation	(4,448)
Proceeds from exercise of warrants		3,209,423
Proceeds from exercise of stock options	297,563	368,185
Net cash provided by (used in) financing activities	293,115	57,350,168
Net increase (decrease) in cash and cash equivalents	(40,937,302)	43,603,638
Cash and cash equivalents - beginning of period	57,496,702	13,893,064
Cash and cash equivalents - end of period	16,559,400	57,496,702
Non-cash investing and financing activities:
Unrealized gain (loss) on available-for-sale securities	$ (20,248)
Exercise of liability classified warrants for common stock		$ 309,130

Organization and Description of Business

12 Months Ended

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Organization and Description of Business

1.	Organization and Description of Business.

Catalyst Pharmaceuticals, Inc. and subsidiary (collectively, the “Company”), is a development-stage biopharmaceutical company focused on developing and commercializing innovating therapies for people with rare debilitating, chronic neuromuscular and neurological diseases, including Lambert-Eaton Myasthenic Syndrome (LEMS), Congenital Myasthenic Syndromes (CMS), and MuSK antibody positive myasthenia gravis (MuSK-MG). The Company (f/k/a Catalyst Pharmaceutical Partners, Inc.) was incorporated in Delaware in July 2006. It is the successor by merger to Catalyst Pharmaceutical Partners, Inc., a Florida corporation, which commenced operations in January 2002.

On November 28, 2018, the U.S. Food and Drug Administration, or FDA, granted approval of Firdapse^® for the treatment of adults with LEMS.

Since inception, the Company has devoted substantially all of its efforts to business planning, research and development, recruiting management and technical staff, acquiring operating assets and raising capital. The Company’s primary focus is on the development and commercialization of its drug candidates. The Company has incurred operating losses in each period from inception through December 31, 2018. The Company has been able to fund its cash needs to date primarily through public and private offerings of its securities. See Note 11.

Capital Resources

While there can be no assurance, based on currently available information, the Company estimates that it currently has sufficient resources to support its operations for at least the next 12 months from the issuance date of this Form 10-K.

The Company may raise required funds in the future through public or private equity offerings, debt financings, corporate collaborations, governmental research grants or other means. The Company may also seek to raise new capital to fund additional product development efforts, even if it has sufficient funds for its planned operations. Any sale by the Company of additional equity or convertible debt securities could result in dilution to the Company’s current stockholders. There can be no assurance that any such required additional funding will be available to the Company at all or available on terms acceptable to the Company. Further, to the extent that the Company raises additional funds through collaborative arrangements, it may be necessary to relinquish some rights to the Company’s drug candidates or grant sublicenses on terms that are not favorable to the Company. If the Company is not able to secure additional funding when needed, the Company may have to delay, reduce the scope of, or eliminate one or more research and development programs, which could have an adverse effect on the Company’s business.

Basis of Presentation and Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Basis of Presentation and Significant Accounting Policies

2.	Basis of Presentation and Significant Accounting Policies.

PRINCIPLES OF CONSOLIDATION. The consolidated financial statements include the Company’s accounts and those of its wholly-owned subsidiary Catalyst Pharmaceuticals Ireland, Ltd. (“Catalyst Ireland”). All intercompany accounts and transactions have been eliminated in consolidation. Catalyst Ireland was organized in 2017.

USE OF ESTIMATES. The preparation of financial statements in conformity with U.S. generally accepted accounting principles (U.S. GAAP) requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates.

CASH AND CASH EQUIVALENTS. The Company considers all highly liquid instruments, purchased with an original maturity of three months or less, to be cash equivalents. Cash equivalents consist mainly of money market funds. The Company has substantially all of its cash and cash equivalents deposited with one financial institution. These amounts at times may exceed federally insured limits.

INVESTMENTS. The Company invests in high credit-quality funds in order to obtain higher yields on its cash and investments pending the use of those funds in its business. At December 31, 2018, investments consisted of a short-term bond fund and U.S. Treasuries. At December 31, 2017, investments consisted of a short-term bond fund. Such investments are not insured by the Federal Deposit Insurance Corporation.

Short-term bond fund

The short-term bond fund is classified as trading securities. Trading securities are recorded at fair value based on the closing market price of the security. For trading securities, the Company recognizes realized gains and losses and unrealized gains and losses to earnings. At December 31, 2018 and 2017, the only investment classified as trading securities was the short-term bond fund. Unrealized gain (loss) on trading securities was ($29,430) and $29,430, respectively, for the years ended December 31, 2018, and 2017 and is included in other income, net in the accompanying consolidated statements of operations.

U.S. Treasuries

U.S. Treasuries are classified as available-for-sale securities. The Company classifies available-for-sale securities with stated maturities of greater than three months and less than one year from the date of purchase as short-term investments. Available-for-sale securities with stated maturities greater than one year are classified as non-current investments in the accompanying consolidated balance sheets. The Company records available-for-sale securities at fair value with unrealized gains and losses in accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses are included in other income, net in the consolidated statements of operations and are derived using the specific identification method for determining the cost of securities sold. Interest income is recognized when earned and is included in other income, net in the consolidated statements of operations. The Company recognizes a charge when the declines in the fair value below the amortized cost basis of its available-for-sale securities are judged to be other-than-temporary. The Company considers various factors in determining whether to recognize an other-than-temporary charge, including whether the Company intends to sell the security or whether it is more likely than not that the Company would be required to sell the security before recovery of the amortized cost basis. The Company has not recorded any other-than-temporary impairment charges on its available-for-salesecurities. See Note 3.

INVENTORY. Inventories are stated at the lower of cost or net realizable value with cost determined under the first-in-first-out (FIFO) cost method. Inventories consist of raw materials and supplies, work in process and finished goods. Costs to be capitalized as inventories include third party manufacturing costs, associated compensation related costs of personnel indirectly involved in the manufacturing process and other overhead costs such as ancillary supplies. The Company began capitalizing inventories post FDA approval of Firdapse^® on November 28, 2018 as the related costs were expected to be recoverable through the commercialization of the product. Costs incurred prior to the FDA approval of Firdapse^® have been recorded as research and development expenses in the consolidated statements of operations. If information becomes available that suggests that inventories may not be realizable, the Company may be required to expense a portion or all of the previously capitalized inventories. The costs of inventories during the year ended December 31, 2018 consists mainly of packaging and labeling costs, indirect costs including compensation cost of personnel and supplies. As of December 31, 2018, inventory was approximately $56,000. As of December 31, 2017, the Company did not have any inventory.

Products that have been approved by the FDA or other regulatory authorities, such as Firdapse^®, are also used in clinical programs to assess the safety and efficacy of the products for usage in treating diseases that have not been approved by the FDA or other regulatory authorities. The form of Firdapse^® utilized for both commercial and clinical programs is identical and, as a result, the inventory has an “alternative future use” as defined in authoritative guidance. Raw materials and purchased drug product associated with clinical development programs are included in inventory and charged to research and development expense when the product enters the research and development process and no longer can be used for commercial purposes and, therefore, does not have an “alternative future use”.

The Company evaluates for potential excess inventory by analyzing current and future product demand relative to the remaining product shelf life. The Company builds demand forecasts by considering factors such as, but not limited to, overall market potential, market share, market acceptance, and patient usage.

PREPAID EXPENSES AND OTHER CURRENT ASSETS. Prepaid expenses and other current assets consist primarily of prepaid research fees, prepaid insurance, prepaid pre-commercialization fees, and prepaid subscription fees. Prepaid research fees consist of advances for the Company’s product development activities, including drug manufacturing, contracts for preclinical studies, clinical trials and studies, regulatory affairs, and consulting. Such advances are recorded as expense as the related goods are received or the related services are performed.

PROPERTY AND EQUIPMENT. Property and equipment are recorded at cost. Depreciation is calculated to amortize the depreciable assets over their useful lives using the straight-line method and commences when the asset is placed in service. Leasehold improvements are amortized on a straight-line basis over the term of the lease or the estimated life of the improvement, whichever is shorter. Useful lives generally range from three to five years for computer equipment to five years for furniture and equipment, and from four to seven years for leasehold improvements. Expenditures for repairs and maintenance are charged to expenses as incurred.

OPERATING LEASES. The Company recognizes lease expense on a straight-line basis over the lease term. For leases that contain rent holidays, escalation clauses or tenant improvement allowances, the Company recognizes rent expense on a straight-line basis and records the difference between the rent expense and rental amount payable as deferred rent. As of December 31, 2018, and 2017, the Company had $188,207 and $181,467, respectively, of deferred rent and lease incentive in accrued expenses and other liabilities in the consolidated balance sheet.

FAIR VALUE OF FINANCIAL INSTRUMENTS. The Company’s financial instruments consist of cash and cash equivalents, investments, accounts payable, and accrued expenses and other liabilities. At December 31, 2018 and 2017, the fair value of these instruments approximated their carrying value.

FAIR VALUE MEASUREMENTS. Current Financial Accounting Standards Board (FASB) fair value guidance emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Therefore, a fair value measurement should be determined based on the assumptions that market participants would use in pricing the asset or liability. As a basis for considering market participant assumptions in fair value measurements, current FASB guidance establishes a fair value hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity (observable inputs that are classified within Levels 1 and 2 of the hierarchy) and the reporting entity’s own assumptions that it believes market participants would use in pricing assets or liabilities (unobservable inputs classified within Level 3 of the hierarchy).

Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates, foreign exchange rates, and yield curves that are observable at commonly quoted intervals. Level 3 inputs are unobservable inputs for the asset or liability, which are typically based on an entity’s own assumptions, as there is little, if any, related market activity. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the asset or liability.


	Fair Value Measurements at Reporting Date Using
	Balances as of December 31, 2018		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents:
Money market funds	$	14,462,087	$	14,462,087	$	—	$	—

Short-term investments:
Short-term bond fund	$	26,541,349	$	26,541,349	$	—	$	—

U.S. Treasuries	$	10,380,864	$	—	$	10,380,864	$	—

Investments:
U.S. Treasuries	$	5,008,243	$	—	$	5,008,243	$	—


	Balances as of December 31, 2017		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents:
Money market funds	$	56,820,688	$	56,820,688	$	—	$	—

Short-term investments:
Short-term bond fund	$	26,516,711	$	26,516,711	$	—	$	—

WARRANTS LIABILITY. In October 2011, the Company issued 1,523,370 warrants (the 2011 warrants) to purchase shares of the Company’s common stock in connection with a registered direct offering. During the period that the 2011 warrants were outstanding, the Company accounted for these warrants as a liability measured at fair value due to a provision included in the warrants agreement that provided the warrants holders with an option to require the Company (or its successor) to purchase their warrants for cash in an amount equal to their Black-Scholes Option Pricing Model (the Black-Scholes Model) value in the event that certain fundamental transactions, as defined, occurred. The fair value of the warrants liability was estimated using the Black-Scholes Model which required inputs such as the expected term of the warrants, share price volatility and risk-free interest rate. These assumptions were reviewed on a quarterly basis and changes in the estimated fair value of the outstanding warrants were recognized each reporting period in the “Change in fair value of warrants liability” line in the consolidated statements of operations. All unexercised 2011 warrants expired on May 2, 2017.

The following table rolls forward the fair value of the Company’s warrants liability activity for the year ended December 31, 2017. On May 2, 2017, all outstanding and unexercised 2011 warrants expired.


	2017
Fair value, beginning of period	$	122,226
Issuance of warrants		—
Exercise of warrants		(309,130	)
Change in fair value		186,904

Fair value, end of period	$	—

During the year ended December 31, 2017, 613,913 of the 2011 warrants were exercised, with proceeds of $798,087 to the Company.

REVENUES FROM COLLABORATIVE ARRANGEMENT. The Company has entered into a collaboration agreement for the further development and commercialization of generic Sabril^® (vigabatrin) tablets. Pursuant to the terms of this agreement, collaborators could be required to make various payments to the Company, including upfront license fees, milestone payments based on achievement of regulatory approvals, and royalties on sales of products resulting from collaborative agreement.

Nonrefundable upfront license fees are recognized upon receipt as persuasive evidence of an arrangement exists, the price to the collaborator is fixed or determinable and collectability is reasonably assured. An upfront license fee of $500,000 was recognized in the year ended December 31, 2018 when it was paid following execution of the collaborative arrangement for vigabatrin tablets.

Refer to Note 7, Collaborative Arrangement, for further discussion on the Company’s collaborative arrangement.

RESEARCH AND DEVELOPMENT. Costs incurred in connection with research and development activities are expensed as incurred. These costs consist of direct and indirect costs associated with specific projects as well as fees paid to various entities that perform research related services for the Company.

STOCK-BASED COMPENSATION. The Company recognizes expense in the consolidated statements of operations for the fair value of all stock-based payments to employees, directors, scientific advisors and consultants, including grants of stock options and other share-based awards. For stock options, the Company uses the Black-Scholes option valuation model, the single-option award approach, and the straight-line attribution method. Using this approach, compensation cost is amortized on a straight-line basis over the vesting period of each respective stock option, generally one to five years. Forfeitures are recognized as a reduction of stock-based compensation expense as they occur.

CONCENTRATION OF CREDIT RISK. The financial instruments that potentially subject the Company to concentration of credit risk are cash equivalents (i.e. money market funds) and investments. The Company places its cash equivalents with high-credit quality financial institutions. These amounts at times may exceed federally insured limits. The Company has not experienced any credit losses in these accounts.

INCOME TAXES. The Company utilizes the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on differences between the financial reporting and tax basis of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized.

The Company recognizes the financial statement benefit of a tax position only after determining that the relevant tax authority would more likely than not sustain the position following an audit. For tax positions meeting the more-likely-than-not threshold, the amount recognized in the financial statements is the largest benefit that has a greater than 50 percent likelihood of being realized upon ultimate settlement with the relevant tax authority. The Company is subject to income taxes in the U.S. federal jurisdiction and various state jurisdictions. Tax regulations within each jurisdiction are subject to the interpretation of the related tax laws and regulations and require significant judgment to apply. The Company is not subject to U.S. federal, state and local tax examinations by tax authorities for years before 2015. If the Company were to subsequently record an unrecognized tax benefit, associated penalties and tax related interest expense would be reported as a component of income tax expense.

On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the “Tax Act”). The Tax Act makes broad and complex changes to the U.S. tax code, including, but not limited to, (1) reducing the U.S. federal corporate tax rate from 35 to 21 percent; (2) requiring companies to pay a one-time transition tax on certain repatriated earnings of foreign subsidiaries; (3) generally eliminating U.S. federal income taxes on dividends from foreign subsidiaries; (4) requiring a current inclusion in U.S. federal taxable income earnings of controlled foreign corporations; (5) eliminating the corporate alternative minimum tax (AMT) and changing how existing AMT credits can be realized; (6) creating the base erosion anti-abuse tax (BEAT), a new minimum tax; (7) creating a new limitation on deductible interest expense, and (8) changing rules related to uses and limitations of net operating loss carryforwards created in tax years beginning after December 31, 2017.

COMPREHENSIVE INCOME (LOSS). U.S. GAAP requires that all components of comprehensive income (loss) be reported in the financial statements in the period in which they are recognized. Comprehensive income (loss) is net income (loss), plus certain other items that are recorded directly into stockholders’ equity. The Company’s comprehensive loss is shown on the Consolidated Statements of Operations and Comprehensive Loss for the year ended December 31, 2018 and is comprised of net unrealized losses on the Company’s available-for-sale securities. For December 31, 2017 and all prior periods, the Company’s net loss equaled comprehensive loss, since the Company had no items which were considered other comprehensive income (loss).

NET LOSS PER SHARE. Basic net loss per share is computed by dividing net loss for the period by the weighted average number of common shares outstanding during the period. The calculation of basic and diluted net loss per share is the same for all periods presented, as the effect of potential common stock equivalents is anti-dilutive due to the Company’s net loss position for all periods presented. The potential shares, which are excluded from the determination of basic and diluted net loss per share as their effect is anti-dilutive, are as follows:


	2018		2017
Options to purchase common stock		10,532,500		5,191,666

Potential equivalent common stock excluded		10,532,500		5,191,666

Potentially dilutive stock options to purchase common stock as of December 31, 2018, had exercise prices ranging from $0.79 to $4.64. Potentially dilutive stock options to purchase common stock as of December 31, 2017 had exercise prices ranging from $0.47 to $4.64.

SEGMENT INFORMATION. Management has determined that the Company operates in one reportable segment, which is the development and commercialization of pharmaceutical products.

RECLASSIFICATIONS. Certain prior year amounts in the consolidated financial statements have been reclassified to conform to the current year presentation.

RECENTLY ISSUED ACCOUNTING STANDARDS. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The Company adopted the standard as of January 1, 2019, the beginning of fiscal 2019, using the modified retrospective approach in which prior comparative periods are not adjusted. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allows the Company to carry forward historical lease classification. The Company has operating leases for its office facilities, which expire on November 30, 2022. As of January 1, 2019, the Company will recognize an additional asset and corresponding liability related to its facility lease on the consolidated balance sheet of approximately $1.0M to $1.5M. The difference between the additional lease assets and lease liabilities, net of the deferred tax impact, was recorded as an adjustment to accumulated deficit. The standard did not materially impact the Company’s consolidated statement of operations and had no impact on cash flows.

In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. Under this new guidance, modification accounting is required if the fair value, vesting conditions, or classification of the award changes as a result of the change in terms or conditions. ASU 2017-09 is effective for all entities for annual reporting periods beginning after December 15, 2017, including interim reporting periods within each annual reporting period, applied prospectively on or after the effective date. The Company adopted this standard in the first quarter of 2018. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements.

In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting that largely aligns the accounting for share-based payment awards issued to employees and nonemployees. Under this ASU, most of the guidance on such payments to nonemployees would be aligned with the requirements for share-based payments granted to employees. ASU 2018-07 is effective for all entities for annual reporting periods beginning after December 15, 2018, including interim reporting periods within each annual reporting period, with early adoption permitted. The Company has adopted this standard in the first quarter of 2019. The adoption of this standard will not have a material impact on the Company’s consolidated financial statements.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments — Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments. The standard amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses for most financial assets and certain other instruments that aren’t measured at fair value through net income. For available-for-sale debt securities, entities will be required to recognize an allowance for credit losses rather than a reduction in carrying value of the asset. Entities will no longer be permitted to consider the length of time that fair value has been less than amortized cost when evaluating when credit losses should be recognized. The Company plans to adopt the new guidance on January 1, 2020. The Company does not anticipate the adoption will have a material impact on its consolidated financial position or results of operations.

Investments

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Investments

3.	Investments.

Available-for-sale investments by security type were as follows:


	Amortized cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
At December 31, 2018:
U.S. Treasuries – ST	$	10,382,699	$	—	$	(1,835	)	$	10,380,864
U.S. Treasuries – LT		5,026,656		—		(18,413	)		5,008,243

Total	$	15,409,355	$	—	$	(20,248	)	$	15,389,107

At December 31, 2017, the Company did not have any available-for-sale securities.

In accordance with FASB ASC Topic 320, “Investments – Debt and Equity Securities”, or ASC 320, the Company has classified its U.S. Treasuries as available-for-sale securities with secondary or resale markets, and, as such, they are reported at fair value with unrealized gains and losses included in comprehensive loss in stockholders’ equity and realized gain and losses, included in other income, net. There were no realized gains or losses from sales of available-for-sale securities for the years ended December 31, 2018 or 2017.

Certain U.S. Treasuries at December 31, 2018 had fair values less than their amortized costs and, therefore, contained unrealized losses. Given that the Company has no intent to sell the U.S. Treasuries until a recovery of the fair value, which may be at maturity, and there are no current requirements to sell any of these securities, as of December 31, 2018, the Company did not consider these investments to be other-than-temporarily impaired. The Company anticipates full recovery of amortized costs with respect to these investments at maturity. The duration of time the U.S. Treasuries have been in a continuous unrealized loss position as of December 31, 2018 was less than 12 months.

The estimated fair values of available-for-sale securities at December 31, 2018, by contractual maturity, are summarized as follows:


	2018
Due in one year or less	$	10,380,864
Due after one year but within two years		5,008,243

	$	15,389,107

Prepaid Expenses and Other Current Assets

12 Months Ended

Dec. 31, 2018

Text Block [Abstract]

Prepaid Expenses and Other Current Assets

4.	Prepaid Expenses and Other Current Assets.

Prepaid expenses and other current assets consist of the following as of December 31:


	2018		2017
Prepaid research fees	$	358,209	$	388,977
Prepaid insurance		800,261		638,139
Prepaid pre-commercialization fees		17,030		65,000
Prepaid subscriptions fees		170,552		23,347
Prepaid rent		31,561		—
Other		272,168		58,281

Total prepaid expenses and other current assets	$	1,649,781	$	1,173,744

Property and Equipment, net

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property and Equipment, net

5.	Property and Equipment, net.

Property and equipment, net consists of the following as of December 31:


	2018			2017
Computer equipment	$	52,704		$	27,915
Furniture and equipment		212,451			169,931
Leasehold improvements		177,417			152,708

		442,572			350,554
Less: Accumulated depreciation		(197,147	)		(159,169	)

Total property and equipment, net	$	245,425		$	191,385

Depreciation expense was $37,978 and $45,689, respectively, for the years ended December 31, 2018 and 2017.

Accrued Expenses and Other Liabilities

12 Months Ended

Dec. 31, 2018

Payables and Accruals [Abstract]

Accrued Expenses and Other Liabilities

6.	Accrued Expenses and Other Liabilities.

Accrued expenses and other liabilities consist of the following as of December 31:


	2018		2017
Accrued preclinical and clinical trial expenses	$	821,633	$	970,649
Accrued professional fees		1,311,061		227,457
Accrued compensation and benefits		1,941,449		821,935
Accrued license fees		3,000,000		252,500
Deferred rent and lease incentive		33,408		24,011
Other		66,436		24,035

Current accrued expenses and other liabilities		7,173,987		2,320,587
Deferred rent and lease incentive – non-current		154,799		157,456

Non-current accrued expenses and other liabilities		154,799		157,456

Total accrued expenses and other liabilities	$	7,328,786	$	2,478,043

Collaborative Arrangement

12 Months Ended

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborative Arrangement

7.	Collaborative Arrangement.

In December 2018, the Company entered into a collaboration and license agreement with Endo International plsc’s subsidiary, Endo Ventures Limited (EVL), for the further development and commercialization of generic Sabril^® (vigabatrin) tablets through Endo’s U.S. Generic Pharmaceuticals segment, doing business as Par Pharmaceutical.

EVL assumes all development, manufacturing, clinical, regulatory, sales and marketing costs under the collaboration, while the Company is responsible for exercising commercially reasonable efforts to develop, or cause the development of, a final finished, stable dosage form of generic Sabril^®tablets.

Under the terms of the Collaboration, the Company has received an up-front payment, and will receive milestone payments based on achievement of regulatory approvals, and a sharing of defined net profits upon commercialization from EVL consisting of a mid-double digit percent of net sales of generic Sabril^®. Unless terminated earlier in accordance with its terms, the collaboration continues in effect until the date that is ten years following the commercial launch. As of December 31, 2018, a $500,000 upfront license fee was recognized.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

8.	Commitments and Contingencies.

The Company has contracted with drug manufacturers and other vendors, including clinical research organizations (CRO) overseeing one or more of the clinical trials of the Company’s drug candidates, to assist in the execution of the Company’s preclinical and clinical trials, analysis, and the preparation of material necessary for the submission of new drug applications (NDAs) and abbreviated new drug applications (ANDAs) with the U.S. FDA. The contracts are cancelable at any time, but obligate the Company to reimburse the providers for any time or costs incurred through the date of termination.

The Company has executed operating lease agreements for its corporate office. The leases have free and escalating rent payment provisions. The Company recognizes rent expense under such leases on a straight-line basis over the term of the lease. As of December 31, 2018, future minimum lease payments under the operating lease agreements are as follows:


2019	$	329,725
2020		339,612
2021		349,792
2022		329,662

	$	1,348,791

In August 2018, the Company entered into a fourth amendment to the lease to its corporate offices to obtain additional space for its operations. The Company now leases approximately 7,800 square feet and the lease term expires in November 2022. In connection with the expansion, approximately $13,000 of tenant build-out costs were funded and paid by the landlord through lease incentives. The lease incentives are being amortized over the term of the lease as a reduction of rent expense. The lease provides for fixed increases in minimum annual rent payments, as well as rent free periods. The total amount of rental payments due over the lease term is being charged to rent expense on the straight-line method over the term of the lease. The differences between rent expense recorded and the amount paid is credited or charged to accrued expenses and other liabilities in the accompanying consolidated balance sheets. Rent expense was $242,155 and $204,170 respectively, for the years ended December 31, 2018 and 2017.

There are no obligations under capital leases.

On August 27, 2009, the Company entered into a license agreement with Northwestern University (Northwestern), under which it acquired worldwide rights to CPP-115. As of December 31, 2018, the Company had paid $424,885 in connection with the license and had accrued license fees of $0 in the accompanying December 31, 2018 consolidated balance sheet for expenses, maintenance fees and milestones.

In 2018, the Company became aware that certain patents granted to Northwestern in 2018 (which patents have been licensed by Northwestern to a third-party) for a new GABA aminotransferase inhibitor were derived from CPP-115. As a result, the Company terminated the license agreement, based on the Company’s position that Northwestern has violated the license agreement because of its failure to transfer these new patent rights to the Company as part of the existing license agreement. It is also the Company’s position that Northwestern’s publication of information about the new patents in violation of the license agreement has damaged the Company. On October 26, 2018, the Company filed a claim for damages in arbitration against Northwestern for Northwestern’s breaches of the license agreement.

On November 5, 2018, Northwestern advised the Company that in its view, Northwestern has a right to terminate the license agreement with the Company because the Company has allegedly breached the license agreement by failing to pay certain milestones and by allegedly failing to use commercially reasonable efforts to develop and commercialize any products. Northwestern has also advised the Company that, in its view, the Company has engaged in wrongful conduct and communications with the third party that licensed the new patents from Northwestern, and that such communications have damaged Northwestern’s relationship with that third party. The Company disputes Northwestern’s allegations and is vigorously defending itself against claims that Northwestern has brought against it in the arbitration proceeding.

There can be no assurance as to the outcome of this matter.

The Company has an employment agreement with its Chief Executive Officer. Under this agreement, the CEO received an annual base salary of approximately $525,000 in 2018. This agreement expires in November 2020.

Agreements

12 Months Ended

Dec. 31, 2018

Text Block [Abstract]

Agreements

9.	Agreements.

LICENSE AGREEMENT WITH BIOMARIN (FIRDAPSE^®). On October 26, 2012, the Company entered into a license agreement with BioMarin Pharmaceutical, Inc. (BioMarin) for the North American rights to Firdapse^®.

Under the License Agreement, the Company has agreed to pay: (i) royalties to BioMarin for seven years from the first commercial sale of Firdapse^® equal to 7% of net sales (as defined in the license agreement) in North America for any calendar year for sales up to $100 million, and 10% of net sales in North America in any calendar year in excess of $100 million; and (ii) royalties to the third-party licensor of the rights sublicensed to the Company for seven years from the first commercial sale of Firdapse^® equal to 7% of net sales (as defined in the license agreement between BioMarin and the third-party licensor) in any calendar year.

Under the Company’s license agreement with BioMarin, the Company agreed to pay certain milestone payments that BioMarin was obligated to pay to both a third-party licensor of the rights that have been sublicensed to us and to the former stockholders of Huxley Pharmaceuticals (“Huxley”) under an earlier stock purchase agreement between BioMarin and the former Huxley stockholders.

In full satisfaction of the milestone obligations, the Company has paid (i) $3,150,000 in milestone payments to the third party licensor of the rights that have been sublicensed to the Company ($3.0 million of which was paid in February 2019 and the balance of which was paid in 2018) and (ii) $2.0 million in milestone payments to the former Huxley Stockholders (all of which was paid in 2018).

In the BioMarin License Agreement, the Company agreed to share in the cost of certain post-marketing studies of Firdapse^® that were being conducted by BioMarin, and the Company fulfilled its commitment to BioMarin regarding all such payments several years ago.

AGREEMENTS FOR DRUG DEVELOPMENT, PRECLINICAL AND CLINICAL STUDIES. The Company has entered into agreements with contract manufacturers for the manufacture of drug and study placebo for the Company’s trials and studies, with contract research organizations (CRO) to conduct and monitor the Company’s trials and studies and with various entities for laboratories and other testing related to the Company’s trials and studies. The contractual terms of the agreements vary, but most require certain advances as well as payments based on the achievement of milestones. Further, these agreements are cancellable at any time, but obligate the Company to reimburse the providers for any time or costs incurred through the date of termination.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

10.

Income Taxes.

Due to the ongoing operating losses and the inability to recognize any income tax benefit, there is no provision for income taxes in any period presented in these financial statements. Since inception, the Company has only generated pretax losses.

The reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate of 21% to amounts included in the statements of operations is as follows:


	2018			2017
Statutory rate		21.0	%		34.0	%
State tax		4.2	%		3.5	%
Valuation allowance		(25.9	)%		26.5	%
Federal rate change		0.0	%		(73.2	)%
Tax credit		1.4	%		6.8	%
Other		(0.7	)%		2.4	%

		0.0	%		0.0	%

Deferred tax assets and liabilities reflect the net tax effects of net operating loss and tax credit carryovers and the temporary differences between the carrying amounts of assets and liabilities for financial reporting and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets as of December 31, 2018 and 2017 are as follows:


	2018			2017
Net operating loss	$	19,867,591		$	15,718,570
Start-up cost		13,861,147			10,508,487
Tax credits		12,625,275			11,582,134
Deferred compensation		1,919,434			1,326,189
Other		109,779			72,395

Gross deferred tax asset		48,383,226			39,207,775

Valuation allowance		(48,383,226	)		(39,207,775	)

Net deferred tax assets	$	—		$	—

The Company’s deferred tax assets have been fully offset by a valuation allowance at December 31, 2018 and 2017 because the Company believes that it is more likely than not that the deferred tax asset will not be realized. The increase and decrease in the valuation allowance on the deferred tax assets was $9,175,451 and $3,388,951 for the years ended December 31, 2018 and 2017, respectively.

At December 31, 2018 and 2017, respectively, the Company had net operating loss carryforwards of approximately $79.0 million and $62.6 million available to reduce future taxable income, if any. The net operating loss carryforwards will expire at various dates beginning in 2023 and ending in 2037, the amount of net operating loss generated in 2018 will have an infinite life, but will be limited to utilization per year of 80% of taxable income. If an ownership change, as defined under Internal Revenue Code Section 382, occurs, the use of these carry-forwards may be subject to limitation. The effective tax rate of 0% in all periods presented differs from the statutory rate of 21% due to the valuation allowance and because the Company had no taxable income.

Beginning in 2010, the Company has received several orphan drug designations by the FDA for products currently under development. The orphan drug designations allow the Company to claim increased federal tax credits for certain research and development activities.

No interest or penalties were accrued through December 31, 2018. The Company’s policy is to recognize any related interest or penalties in income tax expense. The Company is not subject to U.S. federal, state and local tax examinations by tax authorities for any years before 2015. The Company is not currently under income tax examinations by any tax authorities.

Stockholders' Equity

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Stockholders' Equity

11.

Stockholders’ Equity.

Preferred Stock

The Company has 5,000,000 shares of authorized preferred stock, $0.001 par value per share at December 31, 2018 and 2017. No shares of preferred stock were outstanding at December 31, 2018 and 2017.

Common Stock

The Company has 150,000,000 shares of authorized common stock, par value $0.001 per share. At December 31, 2018 and 2017, 102,739,257 and 102,549,498 shares, respectively, of common stock were issued and outstanding. Each holder of common stock is entitled to one vote of each share of common stock held of record on all matters on which stockholders generally are entitled to vote.

2016 Shelf Registration Statement

On December 23, 2016, the Company filed a shelf Registration Statement on Form S-3 (the 2016 Shelf Registration Statement) with the SEC to sell up to approximately $33.8 million of common stock. The 2016 Shelf Registration Statement (file No. 333-215315) was declared effective by the SEC on January 9, 2017. No sales have been conducted to date under the 2016 Shelf Registration Statement.

2017 Shelf Registration Statement

On July 12, 2017, the Company filed a universal shelf Registration Statement on Form S-3 (the 2017 Shelf Registration Statement) with the SEC to sell up to $150 million of common stock, preferred stock, warrants to purchase common stock, or debt securities (including debt securities that may be convertible or exchangeable for common stock or other securities), which securities may be offered separately or together in units or multiple series. The 2017 Shelf Registration Statement (file No. 333-219259) was declared effective by the SEC on July 26, 2017.

On November 28, 2017, the Company filed a prospectus supplement and offered for sale 16,428,572 shares of its common stock at a price of $3.50 per share in an underwritten public offering under the 2017 Shelf Registration. The Company received gross proceeds in the public offering of approximately $57.5 million before underwriting commission and incurred expenses of approximately $3.7 million.

At December 31, 2018, there is approximately $92.5 million available for future sale under the 2017 Shelf Registration Statement.

Warrant Exercises

All unexercised warrants expired in 2017. For the year ended December 31, 2017, the Company issued 2,257,663 shares of its authorized but unissued common stock upon the exercise of previously issued common stock purchase warrants, with net proceeds to the Company of $3,209,423.

Stockholder Rights Plan

On September 20, 2011, the Board of Directors approved the Company’s adoption of a Stockholder Rights Plan. Under the Plan, a dividend of one preferred share purchase right (a Right) was declared for each share of common stock of the Company that was outstanding on October 7, 2011. Each Right entitles the holder to purchase from the Company one one-hundredth of a share of Series A Junior Preferred Stock at a purchase price of $7.80, subject to adjustment.

The Rights trade automatically with the common stock and will not be exercisable until a person or group has become an “acquiring person” by acquiring 17.5% or more of the Company’s outstanding common stock, or a person or group commences, or publicly announces a tender offer that will result in such a person or group owning 17.5% or more of the Company’s outstanding common stock. Upon announcement that any person or group has become an acquiring person, each Right will entitle all rightholders (other than the acquiring person) to purchase, for the exercise price of $7.80, a number of shares of the Company’s common stock having a market value equal to twice the exercise price. Rightholders would also be entitled to purchase common stock of the acquiring person having a value of twice the exercise price if, after a person had become an acquiring person, the Company were to enter into certain mergers or other transactions. If any person becomes an acquiring person, the Board of Directors may, at its option and subject to certain limitations, exchange one share of common stock for each Right.

The Rights have certain anti-takeover effects, in that they would cause substantial dilution to a person or group that attempts to acquire a significant interest in the Company on terms not approved by the Board of Directors. In the event that the Board of Directors determines a transaction to be in the best interests of the Company and its stockholders, the Board of Directors may redeem the Rights for $0.001 per share at any time prior to a person or group becoming an acquiring person.

On September 19, 2016, the Board of Directors unanimously approved, and on the same date the Company entered into Amendment No. 1 to the Stockholders Rights Plan (the “Amendment”). Under the terms of the Amendment, the outside expiration date of the rights plan has been extended from September 20, 2016 to September 20, 2019. Additionally, as part of the Amendment, the Board adopted a Certificate of Designation, Preferences and Rights of Series A Junior Participating Preferred Stock of the Company to increase the number of shares of Series A Junior Participating Preferred Stock of the Company available for issuance under the Rights Plan from 500,000 shares to 1.5 million shares.

Stock Compensation Plans

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Compensation Plans

12.

Stock Compensation Plans.

For the years ended December 31, 2018 and 2017, the Company recorded stock-based compensation expense as follows:


	2018		2017
Research and development	$	1,079,230	$	785,899
General and administrative		2,471,414		1,622,062

Total stock-based compensation	$	3,550,644	$	2,407,961

The Company may issue stock options, restricted stock, stock appreciation rights and restricted stock units (collectively, the “Awards”) to employees, directors, and consultants of the Company under the 2014 and 2018 Stock Incentive Plans (the 2014 Plan and the 2018 Plan or collectively, the Plans). At December 31, 2018, no shares remain available for future issuance under the 2014 Plan. Under the 2018 Plan, 7,500,000 shares were reserved for issuance and as of December 31, 2018, 3,620,603 shares remain available for future issuance.

Stock Options

The Company has granted stock options to employees, officers, directors, and consultants generally at exercise prices equal to the market price of the common stock at grant date. Option awards generally vest over a period of 1 to 5 years of continuous service and have contractual terms from 5 to 7 years. Certain awards provide for accelerated vesting if there is a change in control. The Company issues new shares as shares are required to be delivered upon exercise of outstanding stock options.

During the years ended December 31, 2018 and 2017, options to purchase 186,665 and 780,000 shares of the Company’s common stock were exercised with gross proceeds to the Company of $297,563 and $368,185, respectively. Further, during the year ended December 31, 2018, no options to purchase shares of the Company’s common stock were exercised on a “cashless” basis. During the year ended December 31, 2017, options to purchase 100,000 shares of the Company’s common stock were exercised on a “cashless” basis, resulting in the issuance of an aggregate of 84,280 shares of the Company’s common stock, respectively.

During the years ended December 31, 2018 and 2017 the Company recorded non-cash stock-based compensation expense related to stock options totaling $3,535,647 and $2,342,625, respectively.

During the years ended December 31, 2018 and 2017, the Company granted seven-year options to purchase an aggregate of 5,822,500 and 1,550,000 shares, respectively, of the Company’s common stock to certain of the Company’s officers, employees, directors, and consultants.

Stock option activity under the Company’s Plans for the year ended December 31, 2018 is summarized as follows:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at beginning of year		5,191,666		$	1.96
Granted		5,822,500			3.04
Exercised or released		(186,665	)		1.59
Forfeited or cancelled		(270,001	)		2.94
Expired		(25,000	)		0.47

Outstanding at end of year		10,532,500		$	2.54		5.39	$	2,239,500

Exercisable at end of year		4,349,996		$	2.16		4.00	$	1,679,297

Other information pertaining to stock option activity during the years ended December 31, 2018 and 2017 was as follows:


	2018		2017
Weighted–average fair value of granted stock options	$	1.93	$	0.91
Total fair value of vested stock options	$	2,193,294	$	2,016,992
Total intrinsic value of exercised stock options	$	274,864	$	2,296,100

The following table summarizes information about the Company’s options outstanding at December 31, 2018:


	Options Outstanding						Options Exercisable
Range of Exercise Prices	Number Outstanding		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price
$0.79 to $1.13		2,385,000		4.78	$	0.99		1,686,664		4.69	$	0.93
$1.14 to $2.28		2,440,000		6.87	$	2.22		209,999		6.22	$	2.07
$2.29 to $3.07		1,765,000		4.84	$	2.60		1,098,333		3.72	$	2.53
$3.08 to $3.75		2,005,000		4.59	$	3.30		995,000		2.71	$	3.14
$3.76 to $4.64		1,937,500		5.62	$	4.03		360,000		3.92	$	4.11

		10,532,500		5.39	$	2.54		4,349,996		4.00	$	2.16

As of December 31, 2018, there was approximately $8.8 million of unrecognized compensation expense related to non-vested stock option awards granted under the Plans. That cost is expected to be recognized over a weighted average period of approximately 2.58 years.

The Company utilizes the Black-Scholes option-pricing model to determine the fair value of stock options on the date of grant. This model derives the fair value of stock options based on certain assumptions related to the expected stock price volatility, expected option life, risk-free interest rate and dividend yield. Expected volatility is based on reviews of historical volatility of the Company’s common stock. The estimated expected option life is based upon estimated employee exercise patterns and considers whether and the extent to which the options are in-the-money. The Company estimates the expected option life for options granted to employees and directors based upon the simplified method. Under this method, the expected life is presumed to be the mid-point between the vesting date and the end of the contractual term. The Company will continue to use the simplified method until it has sufficient historical exercise data to estimate the expected life of the options. The risk-free interest rate assumption is based upon the U.S. Treasury yield curve appropriate for the estimated life of the stock options awards. The expected dividend rate is zero. Forfeitures are recognized as a reduction of stock-based compensation expense as they occur.

Assumptions used during the years were as follows:


	December 31, 2018	December 31, 2017
Risk free interest rate	2.09% to 2.88%	1.66% to 2.25%
Expected term	0 to 7 years	4 to 7 years
Expected volatility	82%	104%
Expected dividend yield	— %	— %
Expected forfeiture rate	— %	— %

Restricted Stock Units

Under the 2018 Plan, participants may be granted restricted stock units, each of which represents a conditional right to receive shares of common stock in the future. The restricted stock units granted under this plan generally vest ratably over a four-year period. Upon vesting, the restricted stock units will convert into an equivalent number of shares of common stock. The amount of expense relating to the restricted stock units is based on the closing market price of the Company’s common stock on the date of grant and is amortized on a straight-line basis over the requisite service period. No restricted stock units were granted during 2018. Restricted stock unit activity during 2017 was as follows:


	2017
	Number of Restricted Stock Units			Weighted Average Grant Date Fair Value
Nonvested balance at beginning of year		26,667		$	2.83
Granted		—			—
Vested		(26,667	)		2.83
Forfeited		—			—

Nonvested balance at end of year		—		$	—

No stock-based compensation related to restricted stocks was recorded during 2018. During the year ended December 31, 2017, the Company recorded non-cash stock-based compensation expense related to restricted stock units totaling $65,336. All restricted stock units were vested as of December 31, 2017.

Common Stock

During the year ended December 31, 2018, the Company granted 3,094 net shares of common stock to an employee as compensation. The Company recorded stock-based compensation related to common stock issued to an employee totaling approximately $15,000, during the year ended December 31, 2018. No shares of common stock were granted during the year ended December 31, 2017.

Quarterly Financial Information (unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information (unaudited)

14.

Quarterly Financial Information (unaudited).

The following table presents unaudited supplemental quarterly financial information for the years ended December 31, 2018 and 2017:


	Quarter Ended
	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
Revenues	$	—		$	—		$	—		$	500,000
Loss from operations	$	(5,933,440	)	$	(6,335,855	)	$	(8,182,603	)	$	(14,843,267	)
Net loss	$	(5,699,892	)	$	(5,965,140	)	$	(7,838,873	)	$	(14,499,609	)
Net loss per share – basic and diluted	$	(0.06	)	$	(0.06	)	$	(0.08	)	$	(0.14	)


	Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
Revenues	$	—		$	—		$	—		$	—
Loss from operations	$	(4,679,871	)	$	(4,181,271	)	$	(4,306,708	)	$	(5,511,786	)
Change in fair value of warrants liability	$	(397,235	)	$	210,331		$	—		$	—
Net loss	$	(4,967,129	)	$	(3,879,901	)	$	(4,177,649	)	$	(5,387,698	)
Net loss per share – basic and diluted	$	(0.06	)	$	(0.05	)	$	(0.05	)	$	(0.06	)

Quarterly basic and diluted net loss per common share were computed independently for each quarter and do not necessarily total to the full year basic and diluted net loss per common share.

Basis of Presentation and Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

PRINCIPLES OF CONSOLIDATION.

USE OF ESTIMATES

CASH AND CASH EQUIVALENTS

INVESTMENTS

Short-term bond fund

U.S. Treasuries

INVENTORY

PREPAID EXPENSES AND OTHER CURRENT ASSETS

PROPERTY AND EQUIPMENT

OPERATING LEASES

FAIR VALUE OF FINANCIAL INSTRUMENTS

FAIR VALUE MEASUREMENTS


	Fair Value Measurements at Reporting Date Using
	Balances as of December 31, 2018		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents:
Money market funds	$	14,462,087	$	14,462,087	$	—	$	—

Short-term investments:
Short-term bond fund	$	26,541,349	$	26,541,349	$	—	$	—

U.S. Treasuries	$	10,380,864	$	—	$	10,380,864	$	—

Investments:
U.S. Treasuries	$	5,008,243	$	—	$	5,008,243	$	—


	Balances as of December 31, 2017		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents:
Money market funds	$	56,820,688	$	56,820,688	$	—	$	—

Short-term investments:
Short-term bond fund	$	26,516,711	$	26,516,711	$	—	$	—

WARRANTS LIABILITY


	2017
Fair value, beginning of period	$	122,226
Issuance of warrants		—
Exercise of warrants		(309,130	)
Change in fair value		186,904

Fair value, end of period	$	—

During the year ended December 31, 2017, 613,913 of the 2011 warrants were exercised, with proceeds of $798,087 to the Company.

REVENUES FROM COLLABORATIVE ARRANGEMENT

Refer to Note 7, Collaborative Arrangement, for further discussion on the Company’s collaborative arrangement.

RESEARCH AND DEVELOPMENT

STOCK-BASED COMPENSATION

CONCENTRATION OF CREDIT RISK

INCOME TAXES

COMPREHENSIVE INCOME (LOSS)

NET LOSS PER SHARE


	2018		2017
Options to purchase common stock		10,532,500		5,191,666

Potential equivalent common stock excluded		10,532,500		5,191,666

SEGMENT INFORMATION

s.	SEGMENT INFORMATION. Management has determined that the Company operates in one reportable segment, which is the development and commercialization of pharmaceutical products.

RECLASSIFICATIONS

t.	RECLASSIFICATIONS. Certain prior year amounts in the consolidated financial statements have been reclassified to conform to the current year presentation.

RECENTLY ISSUED ACCOUNTING STANDARDS

Basis of Presentation and Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Fair Value Measurement Specific to Assets or Liability

The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the asset or liability.


	Fair Value Measurements at Reporting Date Using
	Balances as of December 31, 2018		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents:
Money market funds	$	14,462,087	$	14,462,087	$	—	$	—

Short-term investments:
Short-term bond fund	$	26,541,349	$	26,541,349	$	—	$	—

U.S. Treasuries	$	10,380,864	$	—	$	10,380,864	$	—

Investments:
U.S. Treasuries	$	5,008,243	$	—	$	5,008,243	$	—


	Balances as of December 31, 2017		Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents:
Money market funds	$	56,820,688	$	56,820,688	$	—	$	—

Short-term investments:
Short-term bond fund	$	26,516,711	$	26,516,711	$	—	$	—

Summary of Company's Warrants Liability Activity


	2017
Fair value, beginning of period	$	122,226
Issuance of warrants		—
Exercise of warrants		(309,130	)
Change in fair value		186,904

Fair value, end of period	$	—

Potential Shares Excluded from Determination of Basic and Diluted Net Loss Per Share


	2018		2017
Options to purchase common stock		10,532,500		5,191,666

Potential equivalent common stock excluded		10,532,500		5,191,666

Investments (Tables)

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Summary of Available-for-Sale Investments by Security type

Available-for-sale investments by security type were as follows:


	Amortized cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
At December 31, 2018:
U.S. Treasuries – ST	$	10,382,699	$	—	$	(1,835	)	$	10,380,864
U.S. Treasuries – LT		5,026,656		—		(18,413	)		5,008,243

Total	$	15,409,355	$	—	$	(20,248	)	$	15,389,107

Estimated Fair Values of Available for Sale Securities

The estimated fair values of available-for-sale securities at December 31, 2018, by contractual maturity, are summarized as follows:


	2018
Due in one year or less	$	10,380,864
Due after one year but within two years		5,008,243

	$	15,389,107

Prepaid Expenses and Other Current Assets (Tables)

12 Months Ended

Dec. 31, 2018

Text Block [Abstract]

Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consist of the following as of December 31:


	2018		2017
Prepaid research fees	$	358,209	$	388,977
Prepaid insurance		800,261		638,139
Prepaid pre-commercialization fees		17,030		65,000
Prepaid subscriptions fees		170,552		23,347
Prepaid rent		31,561		—
Other		272,168		58,281

Total prepaid expenses and other current assets	$	1,649,781	$	1,173,744

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property and Equipment, net

Property and equipment, net consists of the following as of December 31:


	2018			2017
Computer equipment	$	52,704		$	27,915
Furniture and equipment		212,451			169,931
Leasehold improvements		177,417			152,708

		442,572			350,554
Less: Accumulated depreciation		(197,147	)		(159,169	)

Total property and equipment, net	$	245,425		$	191,385

Accrued Expenses and Other Liabilities (Tables)

12 Months Ended

Dec. 31, 2018

Payables and Accruals [Abstract]

Schedule of Accrued Expenses and Other Liabilities

Accrued expenses and other liabilities consist of the following as of December 31:


	2018		2017
Accrued preclinical and clinical trial expenses	$	821,633	$	970,649
Accrued professional fees		1,311,061		227,457
Accrued compensation and benefits		1,941,449		821,935
Accrued license fees		3,000,000		252,500
Deferred rent and lease incentive		33,408		24,011
Other		66,436		24,035

Current accrued expenses and other liabilities		7,173,987		2,320,587
Deferred rent and lease incentive – non-current		154,799		157,456

Non-current accrued expenses and other liabilities		154,799		157,456

Total accrued expenses and other liabilities	$	7,328,786	$	2,478,043

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Reconciliation of Income Tax Expense (Benefit) Computed at Statutory Federal Income Tax Rate

The reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate of 21% to amounts included in the statements of operations is as follows:


	2018			2017
Statutory rate		21.0	%		34.0	%
State tax		4.2	%		3.5	%
Valuation allowance		(25.9	)%		26.5	%
Federal rate change		0.0	%		(73.2	)%
Tax credit		1.4	%		6.8	%
Other		(0.7	)%		2.4	%

		0.0	%		0.0	%

Components of Deferred Tax Assets

Significant components of the Company’s deferred tax assets as of December 31, 2018 and 2017 are as follows:


	2018			2017
Net operating loss	$	19,867,591		$	15,718,570
Start-up cost		13,861,147			10,508,487
Tax credits		12,625,275			11,582,134
Deferred compensation		1,919,434			1,326,189
Other		109,779			72,395

Gross deferred tax asset		48,383,226			39,207,775

Valuation allowance		(48,383,226	)		(39,207,775	)

Net deferred tax assets	$	—		$	—

Stock Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation Expense

For the years ended December 31, 2018 and 2017, the Company recorded stock-based compensation expense as follows:


	2018		2017
Research and development	$	1,079,230	$	785,899
General and administrative		2,471,414		1,622,062

Total stock-based compensation	$	3,550,644	$	2,407,961

Stock option activity under the Company's Plans

Stock option activity under the Company’s Plans for the year ended December 31, 2018 is summarized as follows:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at beginning of year		5,191,666		$	1.96
Granted		5,822,500			3.04
Exercised or released		(186,665	)		1.59
Forfeited or cancelled		(270,001	)		2.94
Expired		(25,000	)		0.47

Outstanding at end of year		10,532,500		$	2.54		5.39	$	2,239,500

Exercisable at end of year		4,349,996		$	2.16		4.00	$	1,679,297

Schedule of Other Information Pertaining to Stock Option Activity

Other information pertaining to stock option activity during the years ended December 31, 2018 and 2017 was as follows:


	2018		2017
Weighted–average fair value of granted stock options	$	1.93	$	0.91
Total fair value of vested stock options	$	2,193,294	$	2,016,992
Total intrinsic value of exercised stock options	$	274,864	$	2,296,100

Summary of Company's Stock Options Outstanding

The following table summarizes information about the Company’s options outstanding at December 31, 2018:


	Options Outstanding						Options Exercisable
Range of Exercise Prices	Number Outstanding		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price
$0.79 to $1.13		2,385,000		4.78	$	0.99		1,686,664		4.69	$	0.93
$1.14 to $2.28		2,440,000		6.87	$	2.22		209,999		6.22	$	2.07
$2.29 to $3.07		1,765,000		4.84	$	2.60		1,098,333		3.72	$	2.53
$3.08 to $3.75		2,005,000		4.59	$	3.30		995,000		2.71	$	3.14
$3.76 to $4.64		1,937,500		5.62	$	4.03		360,000		3.92	$	4.11

		10,532,500		5.39	$	2.54		4,349,996		4.00	$	2.16

Summary of Stock Options Awards Based on Certain Assumptions

Assumptions used during the years were as follows:


	December 31, 2018	December 31, 2017
Risk free interest rate	2.09% to 2.88%	1.66% to 2.25%
Expected term	0 to 7 years	4 to 7 years
Expected volatility	82%	104%
Expected dividend yield	— %	— %
Expected forfeiture rate	— %	— %

Summary of Restricted Stock Unit Activity

Restricted stock unit activity during 2017 was as follows:


	2017
	Number of Restricted Stock Units			Weighted Average Grant Date Fair Value
Nonvested balance at beginning of year		26,667		$	2.83
Granted		—			—
Vested		(26,667	)		2.83
Forfeited		—			—

Nonvested balance at end of year		—		$	—

Quarterly Financial Information (unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

The following table presents unaudited supplemental quarterly financial information for the years ended December 31, 2018 and 2017:


	Quarter Ended
	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
Revenues	$	—		$	—		$	—		$	500,000
Loss from operations	$	(5,933,440	)	$	(6,335,855	)	$	(8,182,603	)	$	(14,843,267	)
Net loss	$	(5,699,892	)	$	(5,965,140	)	$	(7,838,873	)	$	(14,499,609	)
Net loss per share – basic and diluted	$	(0.06	)	$	(0.06	)	$	(0.08	)	$	(0.14	)


	Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
Revenues	$	—		$	—		$	—		$	—
Loss from operations	$	(4,679,871	)	$	(4,181,271	)	$	(4,306,708	)	$	(5,511,786	)
Change in fair value of warrants liability	$	(397,235	)	$	210,331		$	—		$	—
Net loss	$	(4,967,129	)	$	(3,879,901	)	$	(4,177,649	)	$	(5,387,698	)
Net loss per share – basic and diluted	$	(0.06	)	$	(0.05	)	$	(0.05	)	$	(0.06	)

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail)		1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 01, 2019 USD ($)	Oct. 31, 2011 shares	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) Segment $ / shares	Dec. 31, 2017 USD ($) $ / shares shares
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Maximum maturity period of cash and cash equivalent				Three months
Inventory			$ 56,012	$ 56,012	$ 0
Deferred rent and lease incentive in accrued expenses and other liabilities			188,207	188,207	181,467
Proceeds of Warrants					3,209,423
Upfront license fees			$ 500,000	$ 500,000	$ 0
Statutory rate				21.00%	34.00%
Stock option exercise price range, Minimum \| $ / shares				$ 0.79	$ 0.47
Stock option exercise price range, Maximum \| $ / shares				$ 4.64	$ 4.64
Number of reportable segment \| Segment				1
Lease Expiration Date				Nov. 30, 2022
U.S. federal corporate tax rate [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Statutory rate					35.00%
Furniture and Equipment [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Useful life of assets				5 years
Subsequent Event [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Additional assets	$ 1,000,000
Corresponding liability	$ 1,500,000
October 28, 2011 Warrants [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Warrants issued in offering \| shares		1,523,370
October 28, 2011 Warrants [Member] \| Warrants Liability, at Fair Value [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Warrants expiration date				May 02, 2017
Number of warrants exercised during the period \| shares					613,913
Proceeds of Warrants					$ 798,087
Other Income, Net [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Unrealized gain(loss),trading securities				$ (29,430)	$ 29,430
Minimum [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Minimum amortization period of compensation cost on straight line basis				1 year
Minimum [Member] \| Leasehold Improvements [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Useful life of assets				4 years
Minimum [Member] \| Computer Equipment [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Useful life of assets				3 years
Maximum [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Minimum amortization period of compensation cost on straight line basis				5 years
Maximum [Member] \| Leasehold Improvements [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Useful life of assets				7 years
Maximum [Member] \| Computer Equipment [Member]
Summary Of Basis Of Presentation And Significant Accounting Policies [Line Items]
Useful life of assets				5 years

Basis of Presentation and Significant Accounting Policies - Fair Value Measurement Specific to Assets or Liability (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 5,008,243	$ 0
Short-Term Bond Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments Fair Value Disclosure	26,541,349	26,516,711
U.S. Treasuries [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments Fair Value Disclosure	10,380,864
Investments	5,008,243
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	14,462,087	56,820,688
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] \| Short-Term Bond Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments Fair Value Disclosure	26,541,349	26,516,711
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] \| Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	14,462,087	$ 56,820,688
Significant Other Observable Inputs (Level 2) [Member] \| U.S. Treasuries [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments Fair Value Disclosure	10,380,864
Investments	$ 5,008,243

Basis of Presentation and Significant Accounting Policies - Summary of Company's Warrants Liability Activity (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($)
Fair Value Disclosures [Abstract]
Fair value, beginning of period	$ 122,226
Issuance of warrants	0
Exercise of warrants	(309,130)
Change in fair value	186,904
Fair value, end of period	$ 0

Basis of Presentation and Significant Accounting Policies - Potential Shares Excluded from Determination of Basic and Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential equivalent common stock excluded	10,532,500	5,191,666
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential equivalent common stock excluded	10,532,500	5,191,666

Investment - Summary of Available-for-Sale Investments by Security type (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($)
Net Investment Income [Line Items]
Amortized cost	$ 15,409,355
Gross Unrealized Gains	0
Gross Unrealized Losses	(20,248)
Estimated Fair Value	15,389,107
U.S. Treasuries - ST [Member]
Net Investment Income [Line Items]
Amortized cost	10,382,699
Gross Unrealized Gains	0
Gross Unrealized Losses	(1,835)
Estimated Fair Value	10,380,864
U.S. Treasuries - LT [Member]
Net Investment Income [Line Items]
Amortized cost	5,026,656
Gross Unrealized Gains	0
Gross Unrealized Losses	(18,413)
Estimated Fair Value	$ 5,008,243

Prepaid Expenses and Other Current Assets - Prepaid Expenses and Other Current Assets (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid research fees	$ 358,209	$ 388,977
Prepaid insurance	800,261	638,139
Prepaid pre-commercialization fees	17,030	65,000
Prepaid subscriptions fees	170,552	23,347
Prepaid rent	31,561
Other	272,168	58,281
Total prepaid expenses and other current assets	$ 1,649,781	$ 1,173,744

Property and Equipment, Net - Property and Equipment, Net (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 442,572	$ 350,554
Less: Accumulated depreciation	(197,147)	(159,169)
Total property and equipment, net	245,425	191,385
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	52,704	27,915
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	212,451	169,931
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 177,417	$ 152,708

Accrued Expenses and Other Liabilities - Schedule of Accrued Expenses and Other Liabilities (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued preclinical and clinical trial expenses	$ 821,633	$ 970,649
Accrued professional fees	1,311,061	227,457
Accrued compensation and benefits	1,941,449	821,935
Accrued license fees	3,000,000	252,500
Deferred rent and lease incentive	33,408	24,011
Other	66,436	24,035
Current accrued expenses and other liabilities	7,173,987	2,320,587
Deferred rent and lease incentive - non-current	154,799	157,456
Non-current accrued expenses and other liabilities	154,799	157,456
Total accrued expenses and other liabilities	$ 7,328,786	$ 2,478,043

Collaborative Arrangement - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Collaboration Arrangement Disclosure [Abstract]
Upfront license fee	$ 500,000	$ 500,000	$ 0
Period of collaboration agreement		10 years

Commitments and Contingencies - Future Minimum Lease Payments under Operating Lease Agreement (Detail)	Dec. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019	$ 329,725
2020	339,612
2021	349,792
2022	329,662
Total	$ 1,348,791

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Aug. 31, 2018 USD ($) ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commitments [Line Items]
Area of leased property \| ft²	7,800
Lease expiration date	2022-11
Tenant build-out costs	$ 13,000
Rent expense		$ 242,155	$ 204,170
Obligations under capital leases		0
Accrued license fees		3,000,000	$ 252,500
CEO Employment Agreement [Member]
Commitments [Line Items]
Annual base salary of CEO		$ 525,000
Expiration date of employment agreement		2020-11
Northwestern License Agreement [Member]
Commitments [Line Items]
License fee paid		$ 424,885
Accrued license fees		$ 0

Agreements - Additional Information (Detail) - License Agreement with BioMarin [Member] - USD ($)	1 Months Ended	12 Months Ended
	Feb. 28, 2019	Dec. 31, 2018
License Agreement [Line Items]
Date on which strategic collaboration is entered into		Oct. 26, 2012
Royalty agreement period		7 years
Net sales royalty threshold		$ 100,000,000
Third Party Licensor [Member]
License Agreement [Line Items]
Milestone payment due		3,150,000
Third Party Licensor [Member] \| Subsequent Event [Member]
License Agreement [Line Items]
Milestone payment due	$ 3,000,000
Huxley [Member]
License Agreement [Line Items]
Milestone payment due		$ 2,000,000
Minimum [Member]
License Agreement [Line Items]
Percentage of royalty on net sales		7.00%
Maximum [Member]
License Agreement [Line Items]
Percentage of royalty on net sales		10.00%

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory rate	21.00%	34.00%
Increase (decrease) in valuation allowance on deferred tax assets	$ 9,175,451	$ (3,388,951)
Net operating loss carryforwards	$ 79,000,000	$ 62,600,000
Net operating loss carryforwards expiration date	Beginning in 2023 and ending in 2037
Effective tax rate	0.00%	0.00%
Percentage of limited utilization of taxable income per year	80.00%
Interest or penalties accrued	$ 0

Income Taxes - Schedule of Reconciliation of Income Tax Expense (Benefit) Computed at Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory rate	21.00%	34.00%
State tax	4.20%	3.50%
Valuation allowance	(25.90%)	26.50%
Federal rate change	0.00%	(73.20%)
Tax credit	1.40%	6.80%
Other	(0.70%)	2.40%
Reconciliation of income tax expense (benefit)	0.00%	0.00%

Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Components of Deferred Tax Assets [Abstract]
Net operating loss	$ 19,867,591	$ 15,718,570
Start-up cost	13,861,147	10,508,487
Tax credits	12,625,275	11,582,134
Deferred compensation	1,919,434	1,326,189
Other	109,779	72,395
Gross deferred tax asset	48,383,226	39,207,775
Valuation allowance	(48,383,226)	(39,207,775)
Net deferred tax assets	$ 0	$ 0

Stockholders' Equity (Preferred Stock and Common Stock) - Additional Information (Detail)	Dec. 31, 2018 Vote $ / shares shares	Dec. 31, 2017 $ / shares shares
Equity [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value \| $ / shares	$ 0.001	$ 0.001
Preferred stock, shares outstanding	0	0
Common stock, shares authorized	150,000,000	150,000,000
Common stock, par value \| $ / shares	$ 0.001	$ 0.001
Common stock, shares issued	102,739,257	102,549,498
Common stock, shares outstanding	102,739,257	102,549,498
Number of votes entitled for each share of common stock \| Vote	1

Stockholders' Equity (2017 Shelf Registration Statement) - Additional Information (Detail) - USD ($)		12 Months Ended
	Nov. 28, 2017	Dec. 31, 2018	Jul. 12, 2017
Underwritten Public Offering [Member]
Stockholders' Equity [Line Items]
Number of common stock sold in offering	16,428,572
Common stock issued, price per share	$ 3.50
Gross proceeds from issuance of common stock	$ 57,500,000
Offering expenses	$ 3,700,000
2017 Shelf Registration Statement [Member]
Stockholders' Equity [Line Items]
Maximum dollar amount of securities to be issued under shelf registration statement			$ 150,000,000
Value of common stock available for future sale		$ 92,500,000

Stockholders' Equity (Stockholder Rights Plan) - Additional Information (Detail) - $ / shares	Sep. 19, 2016	Sep. 20, 2011	Dec. 31, 2018
Series A Preferred Stock [Member]
Stockholders' Equity [Line Items]
Preferred share purchase right price		$ 7.80
Series A Preferred Stock [Member] \| Certificate of Designation [Member]
Stockholders' Equity [Line Items]
Junior participating preferred stock shares issued available for issuance under rights agreement, initial			500,000
Junior participating preferred stock shares issued available for issuance under rights agreement, amended			1,500,000
Stockholder Rights Plan [Member]
Stockholders' Equity [Line Items]
Warrants exercise price		$ 7.80
Minimum percentage of outstanding stock acquired by a person or group to trigger Shareholder Rights Plan		17.50%
Stockholders Rights Plan redemption price of right		$ 0.001
Class of warrant or right expiration date	Sep. 20, 2016
Class of warrant or right expiration date, Extended	Sep. 20, 2019

Stock Compensation Plans - Stock-Based Compensation Expense (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 3,550,644	$ 2,407,961
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	1,079,230	785,899
General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 2,471,414	$ 1,622,062

Stock Compensation Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option contractual term	4 years
Number of stock options exercised	186,665
Proceeds from exercise of stock options	$ 297,563	$ 368,185
Common stock unit granted	5,822,500	0
Expected dividend rate	0.00%	0.00%
Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 15,000
Common stock unit granted	3,094
Stock Option [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting period	1 year
Stock option contractual term	5 years
Stock Option [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting period	5 years
Stock option contractual term	7 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 0	$ 65,336
2014 Stock Incentive Plan [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares available for future issuance under the Plan	0
Two Thousand Eighteen Stock Incentive Plan [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for issuance under the Plan	7,500,000
Common stock shares available for future issuance under the Plan	3,620,603
Two Thousand Eighteen Stock Incentive Plan [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting period	4 years
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options exercised	186,665	780,000
Proceeds from exercise of stock options	$ 297,563	$ 368,185
Non-cash stock-based compensation expense	$ 3,535,647	$ 2,342,625
Stock option granted, contractual term	7 years	7 years
Common stock unit granted	5,822,500	1,550,000
Unrecognized compensation expense related to non-vested stock compensation awards granted under the Plan	$ 8,800,000
Expected remaining weighted average vesting period	2 years 6 months 29 days
Expected dividend rate	0.00%
Options to Purchase Common Stock [Member] \| Cashless Basis [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options exercised	0	100,000
Shares issued for cashless option exercise		84,280

Stock Compensation Plans - Summary of Stock Option Activity under the Company's Plan (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of options, Outstanding at beginning of year	5,191,666
Number of options, Granted	5,822,500	0
Number of options, Exercised or released	(186,665)
Number of options, Forfeited or cancelled	(270,001)
Number of options, Expired	(25,000)
Number of options, Outstanding at end of year	10,532,500	5,191,666
Number of options, Exercisable at end of year	4,349,996
Weighted average exercise price, Outstanding at beginning of year	$ 1.96
Weighted average exercise price, Granted	3.04
Weighted average exercise price, Exercised or released	1.59
Weighted average exercise price, Forfeited or cancelled	2.94
Weighted average exercise price, Expired	0.47
Weighted average exercise price, Outstanding at end of year	2.54	$ 1.96
Weighted average exercise price, Exercisable at end of year	$ 2.16
Weighted Average Remaining Contractual Term (Years), Outstanding at end of year	5 years 4 months 20 days
Weighted Average Remaining Contractual Term (Years), Exercisable at end of year	4 years
Aggregate Intrinsic value, Outstanding at end of year	$ 2,239,500
Aggregate Intrinsic value, Exercisable at end of year	$ 1,679,297

Stock Compensation Plans - Schedule of Other Information Pertaining to Stock Option Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted-average fair value of granted stock options	$ 1.93	$ 0.91
Total fair value of vested stock options	$ 2,193,294	$ 2,016,992
Total intrinsic value of exercised stock options	$ 274,864	$ 2,296,100

Stock Compensation Plans - Summary of Company's Stock Options Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices Lower Range	$ 0.79	$ 0.47
Range of Exercise Prices Upper Range	$ 4.64	$ 4.64
Number Outstanding, Options Outstanding	10,532,500
Weighted Average Remaining Contractual Life (Years), Options Outstanding	5 years 4 months 20 days
Weighted Average Exercise Price, Options Outstanding	$ 2.54
Number Exercisable Options Exercisable	4,349,996
Weighted Average Remaining Contractual Life (Years), Options Exercisable	4 years
Weighted Average Exercise Price, Options Exercisable	$ 2.16
$0.79 to $1.13 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices Lower Range	0.79
Range of Exercise Prices Upper Range	$ 1.13
Number Outstanding, Options Outstanding	2,385,000
Weighted Average Remaining Contractual Life (Years), Options Outstanding	4 years 9 months 10 days
Weighted Average Exercise Price, Options Outstanding	$ 0.99
Number Exercisable Options Exercisable	1,686,664
Weighted Average Remaining Contractual Life (Years), Options Exercisable	4 years 8 months 8 days
Weighted Average Exercise Price, Options Exercisable	$ 0.93
$1.14 to $2.28 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices Lower Range	1.14
Range of Exercise Prices Upper Range	$ 2.28
Number Outstanding, Options Outstanding	2,440,000
Weighted Average Remaining Contractual Life (Years), Options Outstanding	6 years 10 months 13 days
Weighted Average Exercise Price, Options Outstanding	$ 2.22
Number Exercisable Options Exercisable	209,999
Weighted Average Remaining Contractual Life (Years), Options Exercisable	6 years 2 months 19 days
Weighted Average Exercise Price, Options Exercisable	$ 2.07
$2.29 to $3.07 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices Lower Range	2.29
Range of Exercise Prices Upper Range	$ 3.07
Number Outstanding, Options Outstanding	1,765,000
Weighted Average Remaining Contractual Life (Years), Options Outstanding	4 years 10 months 2 days
Weighted Average Exercise Price, Options Outstanding	$ 2.60
Number Exercisable Options Exercisable	1,098,333
Weighted Average Remaining Contractual Life (Years), Options Exercisable	3 years 8 months 19 days
Weighted Average Exercise Price, Options Exercisable	$ 2.53
$3.08 to $3.75 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices Lower Range	3.08
Range of Exercise Prices Upper Range	$ 3.75
Number Outstanding, Options Outstanding	2,005,000
Weighted Average Remaining Contractual Life (Years), Options Outstanding	4 years 7 months 2 days
Weighted Average Exercise Price, Options Outstanding	$ 3.30
Number Exercisable Options Exercisable	995,000
Weighted Average Remaining Contractual Life (Years), Options Exercisable	2 years 8 months 15 days
Weighted Average Exercise Price, Options Exercisable	$ 3.14
$3.76 to $4.64 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices Lower Range	3.76
Range of Exercise Prices Upper Range	$ 4.64
Number Outstanding, Options Outstanding	1,937,500
Weighted Average Remaining Contractual Life (Years), Options Outstanding	5 years 7 months 13 days
Weighted Average Exercise Price, Options Outstanding	$ 4.03
Number Exercisable Options Exercisable	360,000
Weighted Average Remaining Contractual Life (Years), Options Exercisable	3 years 11 months 1 day
Weighted Average Exercise Price, Options Exercisable	$ 4.11

Stock Compensation Plans - Summary of Stock Options Awards Based on Certain Assumptions (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate, Minimum	2.09%	1.66%
Risk free interest rate, Maximum	2.88%	2.25%
Expected volatility	82.00%	104.00%
Expected dividend yield	0.00%	0.00%
Expected forfeiture rate	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	0 years	4 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	7 years	7 years

Stock Compensation Plans - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Schedule Of Restricted Stock Activity [Line Items]
Nonvested balance at beginning of year \| shares	26,667
Granted \| shares	0
Vested \| shares	(26,667)
Forfeited \| shares	0
Nonvested Weighted Average Grant Date Fair Value balance at beginning of year \| $ / shares	$ 2.83
Weighted Average Grant Date Fair Value, Granted \| $ / shares	0
Weighted Average Grant Date Fair Value, Vested \| $ / shares	2.83
Weighted Average Grant Date Fair Value, Forfeited \| $ / shares	$ 0

Quarterly Financial Information (Unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 500,000								$ 500,000	$ 0
Loss from operations	(14,843,267)	$ (8,182,603)	$ (6,335,855)	$ (5,933,440)	$ (5,511,786)	$ (4,306,708)	$ (4,181,271)	$ (4,679,871)	(35,295,165)	(18,679,636)
Change in fair value of warrants liability							210,331	(397,235)		(186,904)
Net loss	$ (14,499,609)	$ (7,838,873)	$ (5,965,140)	$ (5,699,892)	$ (5,387,698)	$ (4,177,649)	$ (3,879,901)	$ (4,967,129)	$ (34,003,514)	$ (18,412,377)
Net loss per share - basic and diluted	$ (0.14)	$ (0.08)	$ (0.06)	$ (0.06)	$ (0.06)	$ (0.05)	$ (0.05)	$ (0.06)	$ (0.33)	$ (0.21)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Stockholders' Equity (2016 Shelf Registration Statement) - Additional Information (Detail)	Dec. 23, 2016 USD ($)
2016 Shelf Registration Statement [Member]
Stockholders' Equity [Line Items]
Maximum dollar amount of common stock to be issued under shelf registration statement	$ 33,800,000

Stockholders' Equity (Warrant Exercises) - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) shares
Equity [Abstract]
Issuance of common stock for warrant exercises \| shares	2,257,663
Proceeds from exercise of warrants \| $	$ 3,209,423

Benefit Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Employees contribution of pre-tax annual compensation	15.00%
Discretionary matching contributions of employee contributions of an employee's gross salary	4.00%
Contributions	$ 123,000	$ 84,000

Investments - Additional Information (Detail) - USD ($)	12 Months Ended
Investments - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Realized gains losses from available for sale securities	$ 0	$ 0

Investment - Estimated Fair Values of Available for Sale Securities (Detail)	Dec. 31, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract]
Due in one year or less	$ 10,380,864
Due after one year but within two years	5,008,243
Estimated Fair Value	$ 15,389,107