Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended
	May 31, 2017	Aug. 31, 2016	Dec. 31, 2017	Nov. 30, 2017
Class of Stock [Line Items]
Aggregate value of securities available under shelf registration statement			$ 150,000,000
Helsinn Investment Fund SA | Helsinn Equity Agreement
Class of Stock [Line Items]
Sale of stock, number of common stock issued		2,616,431
Proceeds from sale of equity method investment		$ 5,000,000
Maximum
Class of Stock [Line Items]
Sale of shares and warrants under agreement	$ 150,000,000
Maximum | ATM Sales Agreement
Class of Stock [Line Items]
Sale of shares under agreement				$ 30,000,000