Business - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Apr. 05, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Nature Of Business [Line Items]
Date of formation				Jul. 02, 2004
Proceeds from equity and debt financing		$ 291,100		$ 291,100
Upfront and milestone payments received in connection with license agreements		33,500		33,500
Unrestricted cash and cash equivalents and marketable securities		112,436		112,436
Accumulated deficit		193,720		193,720		$ 162,171
Net loss		$ (9,300)	$ (13,075)	(31,504)	$ (23,766)
Net cash used in operating activities				33,563	$ 21,292
Follow-on Public Offering [Member]
Nature Of Business [Line Items]
Proceeds from offering of common stock				86,224
Follow-on Public Offering [Member] | Common Stock [Member]
Nature Of Business [Line Items]
Proceeds from offering of common stock	$ 86,224			$ 5