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, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income tax provision at statutory rate	$ (16,010)	$ (15,662)	$ (17,013)
Nondeductible items	135	401	456
Change in tax credits	(1,449)	(792)	(678)
Change in valuation allowance	17,824	16,706	17,911
Foreign tax and other	(384)	(487)	(676)
Total provision for income taxes	$ 116	$ 166	$ 0