Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Deferred revenue	$ 7,490	$ 315
Basis difference in equipment	(1,013)	(975)
Basis difference in intangibles	1,122	1,102
Accrued liabilities and other	1,563	360
R&D credit	11,138	11,316
Stock options	1,151	462
Net operating loss carry-forward	63,509	59,481
Gross, Deferred Tax Assets	84,960	72,061
Less: valuation allowance	(84,960)	(72,061)
Net of Valuation Allowance	$ 0	$ 0