Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 18,951	$ 409	$ 199
State	507	40	78
Foreign	2,072	3,482	562
Current income tax expense	21,530	3,931	839
Deferred:
Federal	1,038	(2,357)	88
State	(580)	(229)	9
Foreign	(1,645)	174	(943)
Deferred income tax benefit	(1,187)	(2,412)	(846)
Income tax expense (benefit)	$ 20,343	$ 1,519	$ (7)