Quarterly Financial Data (Unaudited) - 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
Income Statement [Abstract]
Revenue	$ 4,722	$ 7,086	$ 3,535	$ 4,287	$ 2,456	$ 5,346	$ 7,106	$ 8,910	$ 19,630	$ 23,818
Gross loss	(4,891)	(11,646)	(4,051)	(5,419)	(8,988)	(3,891)	(5,155)	(5,109)	(26,008)	(23,143)
Loss from operations	(21,642)	(24,769)	(8,150)	(8,156)	(12,309)	(47,370)	(8,322)	(7,948)	(62,717)	(75,949)
Loss before income taxes	(22,218)	(25,017)	(8,383)	(7,484)	(12,156)	(48,859)	(8,529)	(8,312)	(63,102)	(77,856)
Net loss	$ (22,536)	$ (24,801)	$ (8,209)	$ (7,333)	$ (12,706)	$ (48,196)	$ (8,580)	$ (8,348)	$ (62,879)	$ (77,830)
Basic and diluted loss per common share	$ (0.85)	$ (0.94)	$ (0.31)	$ (0.28)	$ (0.49)	$ (1.84)	$ (0.33)	$ (0.32)	$ (2.39)	$ (2.98)
Weighted average common shares outstanding used in computing net loss per common share, basic and diluted:	26,527,909	26,374,516	26,296,398	26,226,614	26,192,838	26,160,308	26,142,261	26,129,276	26,356,359	26,156,170