Quarterly Financial Data (Unaudited) - Summary of Quarterly Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue	$ 2,456	$ 5,346	$ 7,106	$ 8,910	$ 8,912	$ 8,036	$ 14,469	$ 14,268	$ 23,818	$ 45,685	$ 41,513
Gross loss	(8,988)	(3,891)	(5,155)	(5,109)	(5,459)	(9,460)	(7,274)	(7,494)	(23,143)	(29,687)	(21,921)
Loss from operations	(12,309)	(47,370)	(8,322)	(7,948)	(8,637)	(13,872)	(10,179)	(10,925)	(75,949)	(43,613)	(34,884)
Loss before income taxes	(12,156)	(48,859)	(8,529)	(8,312)	(9,032)	(14,011)	(9,984)	(10,888)	(77,856)	(43,915)	(35,511)
Net loss	$ (12,706)	$ (48,196)	$ (8,580)	$ (8,348)	$ (9,402)	$ (13,713)	$ (9,984)	$ (10,894)	$ (77,830)	$ (43,993)	$ (30,351)
Basic and diluted loss per common share	$ (0.49)	$ (1.84)	$ (0.33)	$ (0.32)	$ (0.36)	$ (0.53)	$ (0.39)	$ (0.43)	$ (2.98)	$ (1.70)
Weighted average common shares outstanding used in computing net loss per common share, basic and diluted:	26,192,838	26,160,308	26,142,261	26,129,276	26,127,026	26,110,651	25,706,797	25,317,147	26,156,170	25,815,405