Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2014
Stockholders Equity [Line Items]
Sale of common stock, preferred stock, debt securities and warrants		$ 100,000,000
Purchase of technology license with common stock		$ 775,000	$ 0	$ 0
Maximum value of common stock issuable under agreement					$ 25,000,000
Number of shares of common stock sold under the sales agreement		0	3,291,521
Gross proceeds from the sales agreement			$ 4,067,751
Sales agreement expiration month and year		2015-05
Astellas In-License Agreements [Member]
Stockholders Equity [Line Items]
Restricted stock issued, shares	861,216
Astellas In-License Agreements [Member] | Collaborative Arrangement [Member]
Stockholders Equity [Line Items]
Restricted stock issued, shares	861,216
Astellas In-License Agreements [Member] | Collaborative Arrangement [Member] | Research and development [Member]
Stockholders Equity [Line Items]
Cash payment for license agreement	$ 250,000
Purchase of technology license with common stock		$ 775,094