Summary of Quarterly Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Collaboration and licensing revenue	$ 127	$ 992	$ 193	$ 1,203	$ 3,598	$ 15,158	$ 134	$ 134	$ 2,515	$ 19,024	$ 18,123
Restructuring and lease exit							25	4,333		4,358	11,729
Operating expenses	9,553	6,585	7,335	8,435	9,721	6,691	4,730	5,950
(Loss) income from operations	(9,426)	(5,593)	(7,142)	(7,232)	(6,123)	8,467	(4,621)	(10,149)	(29,393)	(12,426)	(50,449)
Change in fair value warranty liability	4,569	1,178	(996)						(4,751)
Other expense, net	(748)	(551)	(468)	(378)	(462)	(553)	(835)	(725)	2,607	(2,575)	(2,290)
Net (loss) income	$ (5,605)	$ (4,966)	$ (8,606)	$ (7,710)	$ (6,585)	$ 7,914	$ (5,456)	$ (10,874)	$ (26,887)	$ (15,001)	$ (52,739)
Net (loss) income per share	$ (0.07)	$ (0.07)	$ (0.13)	$ (0.13)	$ (0.11)	$ 0.14	$ (0.10)	$ (0.21)	$ (0.39)	$ (0.27)	$ (1.01)