Analysis of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 138,786	$ 115,699
Difference in depreciation and amortization	2,694	2,800
Research and development tax credits	31,397	29,127
Stock-based compensation	20,774	13,637
Deferred rent	2,771	2,864
Deferred revenue	1,324	1,213
Capitalized inventory	19,018
Other	3,060	413
Gross deferred tax assets	219,824	165,753
Valuation allowance	(219,824)	(165,753)
Net deferred tax assets	$ 0	$ 0