Income Taxes - Income Tax Expense (Benefit) Differed from Amounts Computed by Applying Statutory Federal Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax provision at statutory rate	$ (16,202)	$ (15,076)	$ (16,010)
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings and Other Nondeductible Amounts	195	179	135
Change in tax credits	(2,148)	(2,361)	(1,449)
Change in valuation allowance	19,935	(19,792)	17,824
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	0	37,690	0
Foreign tax and other	(1,531)	(436)	(384)
Total provision for income taxes	$ 249	$ 204	$ 116