Research and License Agreements - Additional Information (Detail)	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2017 USD ($) LicenseAgreement	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2013 USD ($)
University Research Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research agreement date				2013-12
Maximum allowable research and development expenses per year						$ 386,000
Research agreement expiration date				Aug. 31, 2018
Maximum allowable research and development expenses		$ 2,500,000		$ 2,500,000
Payments pursuant to research agreements		$ 0	$ 0	$ 188,000	$ 375,000
License Agreements
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research agreement date				2013-12
Number of license agreements | LicenseAgreement	2
Maximum future contingent license payment	$ 6,400,000
Aggregate potential milestone payments for receipt of regulatory approval	5,000,000
Aggregate potential milestone payments for final regulatory approval of second indication	$ 500,000
License Agreements | Minimum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Rate of revenue share	6.50%
License Agreements | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Rate of revenue share	25.00%