Business - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accounting Policies [Abstract]
Date of formation	Jul. 02, 2004
Proceeds from equity and debt financing	$ 291,100
Upfront and milestone payments received in connection with license agreements	33,500
Unrestricted cash and cash equivalents and marketable securities	74,521
Accumulated deficit	237,108		$ 220,341
Net loss	16,767	$ 22,204
Net cash used in operating activities	$ (18,468)	$ (21,636)