Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current taxes:
U.S. federal									$ 1,868	$ 8,792	$ 19,392
State and local									1,937	1,181	1,939
Foreign									9,968	1,786	13,245
Total current tax expense									13,773	11,759	34,576
Deferred taxes:
U.S. federal									202	14,626	(4,530)
State and local									50	795	(321)
Foreign									5,183	(827)	(2,606)
Total deferred tax (benefit) expense									5,435	14,594	(7,457)
Total tax expense	$ 4,700	$ 3,800	$ 3,300	$ 7,400	$ 24,500	$ (4,400)	$ 3,300	$ 2,900	$ 19,208	$ 26,353	$ 27,119