Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Reserves and accruals	$ 2,014	$ 2,817
Deferred revenue	6,466	10,379
Stock-based compensation	3,747	7,361
Net operating loss carryforwards	35,404	47,452
Loss on OCI	231	370
Depreciation and amortization	565	721
Other	(3)	67
Gross deferred tax assets	48,424	69,167
Valuation allowance	(46,125)	(68,227)
Total deferred tax assets	2,299	940
Deferred tax liabilities:
Stock-based compensation	0	(21)
Depreciation and amortization	(610)	(964)
Total deferred tax liabilities	(610)	(985)
Net deferred tax asset	$ 1,689
Net deferred tax liability		$ (45)