Analysis of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 144,897	$ 174,569
Difference in depreciation and amortization	1,210	2,589
Research and development and other tax credits	44,306	37,812
Stock-based compensation	14,392	16,166
Deferred rent	1,210	2,306
Deferred revenue	904	1,315
Capitalized inventory	22,127	36,282
Other	4,071	3,047
Total deferred tax assets	233,117	274,086
Deferred tax liabilities:
Debt discount	(28,548)
Total deferred tax liabilities	(28,548)
Valuation allowance	(204,569)	(274,086)
Net deferred tax assets	$ 0	$ 0