Income Taxes - Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits including interest and penalties	$ 5,600	$ 3,900
Interest and penalties	500	300	$ 200
Schedule reconciliation of gross unrecognized tax benefits
Balance at beginning of period	3,622	3,469	3,486
Additions as a result of tax provisions taken during the current year	1,489	305	463
Subtractions as a result of tax provisions taken during the prior year	0	0	(161)
Foreign currency translation	90
Foreign currency translation		(93)	(79)
Lapse in statute of limitations	(141)	(67)	(241)
Settlements	0	0	0
Other	21	8	1
Balance at end of period	5,081	3,622	3,469
Unrecognized tax benefits that would impact effective tax rate	5,300	$ 3,600	$ 3,300
Decrease in unrecognized tax benefits is reasonably possible in next 12 months	100
Net adjustment to deferred income tax expense	2,300
Provisional transition tax obligation	$ 2,100