Income Taxes Effect of Each Type of Temporary Difference Comprising Net Differed Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating losses	$ 119,355	$ 110,715
Stock-based compensation	8,113	12,446
Tax credits	7,816	6,378
Other reserves and accrued liabilities	6,344	3,587
Gross deferred tax assets	141,628	133,126
Less: valuation allowance	(140,117)	(131,389)	$ (109,274)
Total deferred tax assets	1,511	1,737
Deferred tax liabilities:
Depreciation and amortization	(1,011)	(1,145)
Other liabilities	(500)	(592)
Total deferred tax liabilities	$ (1,511)	$ (1,737)