Income Taxes - Reconciliation of the Company's Effective Income Tax Rate to the Federal Statutory Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal income tax at the statutory rate	$ 5,518	$ 11,024	$ 12,347
State income taxes, net of federal benefit	339	889	1,061
Difference between statutory and foreign tax rates	(560)	1,521	2,442
Permanent differences	300	(457)	(205)
Research and development	(2,380)	(1,928)	(1,050)
Return to provision adjustment	23	327	(67)
Change in liability for unrecognized tax benefits	7	700	(156)
Excess stock-based compensation benefit	(1,819)	(77)	(144)
Change in valuation allowance	1,949	1,779	1,200
Tax effects of intercompany transactions	(277)	630	0
Adjustments to deferreds resulting from enactment of new tax law	7,601	0	0
Other	(147)	(208)	0
Provision for income taxes	$ 10,554	$ 14,200	$ 15,428
Effective tax rate	66.90%	45.10%	43.60%