Income Taxes - Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax credit carryforwards	$ 67,346	$ 62,096
Net operating loss carryforwards	10,823	9,066
Reserves and accruals not currently deductible for tax purposes	8,957	8,785
Stock-based compensation	6,004	3,432
Other	2,519	6,472
Gross deferred tax assets	95,649	89,851
Depreciation and amortization	(5,493)	(11,075)
Convertible Debt	(7,375)	161
Gross deferred tax liabilities	(12,868)	(10,914)
Deferred tax valuation allowance	(47,102)	(45,506)
Net deferred tax assets	$ 35,679	$ 33,431