Stockholders' Equity (Deficit) - Additional Information (Detail)										1 Months Ended			12 Months Ended		15 Months Ended
	Aug. 24, 2016 USD ($) $ / shares shares	Jun. 20, 2016 shares	Apr. 29, 2016 USD ($) shares	Apr. 27, 2016 $ / shares shares	Apr. 13, 2016 USD ($) $ / shares shares	May 28, 2015 USD ($) shares	May 26, 2015 $ / shares shares	May 04, 2015 USD ($) $ / shares shares	Apr. 28, 2015 $ / shares shares	Apr. 30, 2016 USD ($) $ / shares shares	May 31, 2015 USD ($) $ / shares shares	Feb. 28, 2014 Tranche $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Jan. 22, 2016	Feb. 20, 2014 USD ($)
Equity [Line Items]
Preferred stock, shares authorized													10,000,000	10,000,000	10,000,000
Preferred stock, par value | $ / shares													$ 0.00001	$ 0.00001	$ 0.00001
Preferred stock, shares outstanding													0	0	0
Common stock, shares authorized													300,000,000	300,000,000	300,000,000
Common stock, par value | $ / shares													$ 0.00001	$ 0.00001	$ 0.00001
Number of common stock for issuance in exchange for future services from founders												1,000,000
Common stock price per share | $ / shares												$ 0.01
Number of tranches | Tranche												2
Unrecognized compensation expense | $											$ 61,556						$ 168,000
Common stock shares repurchased											633,810
Repurchase of common stock from stockholders, per share | $ / shares											$ 0.00001
Remaining number of repurchased shares											366,190
Common stock sold			1,125,000		7,500,000					8,625,000
Common stock, price per share | $ / shares					$ 1.25					$ 1.25
Number of additional common shares pursuant to over-allotment option granted to the underwriters					1,125,000
Cash proceeds from common stock issuance | $			$ 1,283,400		$ 7,754,286					$ 9,037,686			$ 11,548,518	$ 25,392,500
Underwriting discounts, commissions and other offering expenses | $			$ 111,600		$ 1,631,964					$ 1,743,564
Repurchase of common stock from stockholders, value | $														$ 38
Granted, Shares													620,818
Accrued license fees | $								$ 29,247,711
Convertible notes payable, current | $													$ 3,269,582		$ 3,269,582
Convertible notes payable, interest | $													$ 34,894		$ 34,894
Warrants sold					7,500,000					8,625,000
Exercise price per share of common stock | $ / shares					$ 1.50					$ 1.50			$ 10.00		$ 10.00
Underwriters grant period option					45 days
Additional warrants granted to underwriters					1,125,000
Additional warrants sold as a result of over allotment exercise					1,125,000
Public offering price per warrant | $ / shares					$ 0.01
Warrants expiry date										Apr. 13, 2021			Apr. 13, 2021
Repayments of notes payable in stock | $													$ 1,200,000
Over-allotment option exercised				1,125,000
Shares issued as commitment fee in connection with Aspire agreement | $													$ 440,278
Shares issued under ESPP													21,616	5,711
Common Stock [Member]
Equity [Line Items]
Common stock sold														3,655,964
Repurchase of common stock														3,802,859
Repurchase of common stock from stockholders, value | $														$ 38
Common stock, shares issued for services														4,882
Minimum [Member] | Loan and Security Agreement [Member]
Equity [Line Items]
Beneficial ownership of company's common stock					49.90%											49.90%
Non-employee Directors [Member]
Equity [Line Items]
Granted, Shares									83,144
Ligand [Member]
Equity [Line Items]
Common stock sold					560,000
Warrants sold					560,000
Ligand [Member] | Loan and Security Agreement [Member]
Equity [Line Items]
Common stock sold					960,000
Warrants sold					960,000
Exercise price per share of common stock | $ / shares					$ 1.50
Warrants expiry date													Apr. 13, 2021
Repayments of notes payable in stock | $					$ 1,200,000
Maxim [Member]
Equity [Line Items]
Cash proceeds from common stock issuance | $													$ 956,518
Maxim [Member] | Common Stock [Member]
Equity [Line Items]
Common stock sold													778,849
Maxim [Member] | Maximum [Member] | Common Stock [Member]
Equity [Line Items]
Sale of common stock, shares		3,748,726
Aspire Capital [Member] | Common Stock [Member] | Stock Purchase Agreement [Member]
Equity [Line Items]
Common stock sold	333,333												150,000
Common stock, price per share | $ / shares	$ 1.50
Cash proceeds from common stock issuance | $													$ 173,250
Common stock sold aggregate purchase price | $	$ 500,000
Common stock purchase agreement term	30 months
Minimum closing sale price per share to execute transactions under agreement | $ / shares	$ 0.40
Common stock issued as consideration for commitment fee	336,116
Shares issued as commitment fee in connection with Aspire agreement | $													$ 440,278
Aspire Capital [Member] | Maximum [Member] | Common Stock [Member] | Stock Purchase Agreement [Member]
Equity [Line Items]
Common stock sold aggregate purchase price | $	$ 12,500,000
IPO [Member]
Equity [Line Items]
Repurchase of common stock from stockholders, per share | $ / shares								$ 0.00001
Anniversary date of closing													May 04, 2015
Common stock sold									3,000,000
Common stock, price per share | $ / shares							$ 8.00		$ 8.00
Underwriters option exercise period													30 days
Number of additional common shares pursuant to over-allotment option granted to the underwriters						450,000			450,000
Cash proceeds from common stock issuance | $						$ 3,225,866		$ 19,100,500
Underwriting discounts, commissions and other offering expenses | $						$ 374,134		$ 4,899,500
Repurchase of common stock								3,802,859
Repurchase of common stock from stockholders, value | $								$ 38
Accrued license fees | $								27,422,872			$ 24,826,374
Non-cash interest charge | $								4,421,338
Convertible notes payable, current | $								310,350
Convertible notes payable, interest | $								$ 24,276
Convertible notes payable and interest conversion, shares issued								57,046
Beneficial conversion charge | $													$ 121,786
Additional shares purchase under underwriting agreement							450,000
IPO [Member] | Accrued License Fees [Member]
Equity [Line Items]
Common stock, shares issued for services								3,427,859
IPO [Member] | Employees, Directors and Consultants [Member]
Equity [Line Items]
Common stock sold													422,879
Granted, Shares													206,000
IPO [Member] | Ligand And Metabasis Therapeutics Inc [Member]
Equity [Line Items]
Common stock sold						228,105
Common stock, shares issued for services								3,427,859
IPO [Member] | Ligand [Member]
Equity [Line Items]
Common stock sold													3,655,964
Common stock sold aggregate purchase price | $													$ 29,200,000
Over-Allotment Option [Member]
Equity [Line Items]
Common stock, price per share | $ / shares				$ 1.24
Warrants sold					1,125,000
Tranche One [Member]
Equity [Line Items]
Number of common stock for issuance in exchange for future services from founders												500,000
Remaining number of repurchased shares											183,095
Stock compensation expense | $													$ 12,371	$ 18,407	$ 30,778
Tranche Two [Member]
Equity [Line Items]
Number of common stock for issuance in exchange for future services from founders												500,000
Remaining number of repurchased shares											183,095