Income Taxes - Provision for Income Taxes (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 taxes:
U.S. federal									$ 8,792	$ 19,392	$ 15,995
State and local									1,181	1,939	3,624
Foreign									1,786	13,245	4,136
Total current tax expense									11,759	34,576	23,755
Deferred taxes:
U.S. federal									14,626	(4,530)	(2,252)
State and local									795	(321)	(759)
Foreign									(827)	(2,606)	(3,047)
Total deferred tax (benefit) expense									14,594	(7,457)	(6,058)
Total tax expense	$ 24,500	$ (4,400)	$ 3,300	$ 2,900	$ 8,700	$ 6,100	$ 10,200	$ 2,100	$ 26,353	$ 27,119	$ 17,697