Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 14, 2017	Apr. 13, 2016	May 04, 2015	Jun. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jan. 16, 2018
Class of Warrant or Right [Line Items]
Issuance of shares of common stock		7,500,000		0	0		0
Exercise price of warrant		$ 1.50	$ 10.00
Warrant description					The warrant was exercisable for cash or on a cashless basis at a per share exercise price equal to $10.00 commencing on April 28, 2016, one year following the date of the prospectus filed with the SEC relating to the IPO, and expiring on April 28, 2020. The warrant was exercised in full during the year ended December 31, 2018. The warrant also provided for registration rights upon request, under certain circumstances. The piggyback registration right provided in connection with the warrant was to terminate on April 28, 2022.
Warrant termination date					Apr. 28, 2022
Initial public offering, expiration date					Apr. 28, 2020
Warrants sold		7,500,000		4,168,238	4,168,238
Common stock, price per share		$ 1.25
Warrants expiry date						Apr. 13, 2021
Public offering price per warrant		$ 0.01
Warrants exercised				116,603	356,363
Securities Purchase Agreement [Member]
Class of Warrant or Right [Line Items]
Warrants sold				885,395	885,395
Warrants exercised					0
Public offering price per share and per warrant	$ 1.15
Unexercised warrants								1,987,337
Loan and Security Agreement [Member] | Minimum [Member]
Class of Warrant or Right [Line Items]
Beneficial ownership of company's common stock		49.90%
Ligand [Member] | Loan and Security Agreement [Member]
Class of Warrant or Right [Line Items]
Exercise price of warrant		$ 1.50
Warrants sold		960,000
Warrants expiry date					Apr. 13, 2021
Repayments of notes payable in stock		$ 1.2
Over Allotment Option [Member]
Class of Warrant or Right [Line Items]
Warrants sold		1,125,000
Private Placement and Registered Direct Offering [Member] | Securities Purchase Agreement [Member]
Class of Warrant or Right [Line Items]
Issuance of shares of common stock	3,749,783
Exercise price of warrant	$ 1.30
Warrants expiry date					Dec. 19, 2022
Number of warrants issued for common stock	0.75
Warrants exercisable date					Dec. 19, 2017
Percentage of warrant exercise beneficial ownership limitation of common stock outstanding minimum	4.99%
Prior notice period of increase beneficial ownership limitation	61 days
Percentage of minimum beneficial ownership limitation	9.99%
Description of beneficial ownership limitation					Each holder of a Warrant will not have the right to exercise any portion of its Warrant if the holder, together with its affiliates, would beneficially own in excess of 4.99% of the number of shares of common stock outstanding immediately after giving effect to such exercise (the “Beneficial Ownership Limitation”); provided, however, that upon 61 days’ prior notice to the Company, the holder may increase the Beneficial Ownership Limitation; however, in no event shall the Beneficial Ownership Limitation exceed 9.99%.
Common stock warrants [Member]
Class of Warrant or Right [Line Items]
Issuance of shares of common stock			82,500
Common Stock [Member] | Private Placement and Registered Direct Offering [Member] | Maximum [Member] | Securities Purchase Agreement [Member]
Class of Warrant or Right [Line Items]
Warrants sold	2,812,337