Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Reserves and accruals	$ 17,090	$ 17,247
Net operating loss carryforwards	29,900	34,915
Research and development credit carryforwards	36,446	34,419
Deferred stock-based compensation	2,201	2,677
Intangibles	2,585	2,062
Other	939	1,441
Gross deferred tax assets	89,161	92,761
Valuation allowance	(77,144)	(77,756)	$ (74,480)	$ (64,545)
Gross deferred tax assets after valuation allowance	12,017	15,005
Deferred tax liabilities:
Depreciation and amortization	(391)	(259)
Convertible notes	(2,931)	(4,284)
Gross deferred tax liabilities	(3,322)	(4,543)
Net deferred tax assets	$ 8,695	$ 10,462