Income Taxes - Components of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Non-deductible reserves and accruals	$ 4,936	$ 8,189
Net operating loss and other carryforwards	8,528	7,560
Stock compensation	2,644	5,327
Depreciation and amortization	402	1,196
Other assets	46	50
Gross deferred tax asset	16,556	22,322
Less - valuation allowance	(2,686)	(2,193)	$ (1,534)	$ (1,565)
Sub-total	13,870	20,129
Other liabilities	(911)	(453)
Goodwill amortization	(5,677)	(5,013)
Deferred commissions	(3,873)	(4,928)
Net deferred tax asset	$ 3,409	$ 9,735