Income Taxes - Reconciliation of Income Taxes Calculated at U.S. Federal Statutory Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income taxes at U.S. federal statutory rate	$ (12,744)	$ 4,796	$ 4,117
Foreign income taxes at rates other than the federal statutory rate	373	(584)	(10)
U.S. state and local income taxes, net of U.S. federal tax benefit	(155)	94	(47)
U.S. Tax Cut and Jobs Act: transition tax, net of foreign tax credits	4,187
Change in valuation allowance	47,429
Foreign withholding taxes	4,181	4,235	3,790
Foreign dividends		5,077	4,152
U.S. foreign tax credit	(4,154)	(8,786)	(9,808)
Research and development tax credit	(2,999)	(2,696)	(1,608)
Domestic production activities deduction		(840)	(833)
Non-deductible stock-based compensation	10,871	2,064	234
Meals & entertainment	358	235	258
Other	(163)	(91)	125
Deferred tax on investment in subsidiary		(264)	(214)
Uncertain tax position	446	299	662
Tax law changes	15,366
Income tax expense	$ 62,996	$ 3,539	$ 818