Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current expense (benefit):
Federal									$ 3,849	$ 1,933	$ (17)
State									645	492	747
Foreign									5,168	3,802	3,218
Total current expense									9,662	6,227	3,948
Deferred expense (benefit):
Federal									(314)	(144)	3,250
State									(216)	(195)	294
Foreign									(774)	(623)	(94)
Total deferred (benefit) expense									(1,304)	(962)	3,450
Total income tax expense	$ 4,474	$ 1,364	$ 1,830	$ 690	$ 2,116	$ (978)	$ 2,572	$ 1,555	$ 8,358	$ 5,265	$ 7,398