Income Taxes Income tax expense, income tax reconciliation (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
Income Taxes [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate									25.00%
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate									$ 25,427	$ 18,652	$ 37,173
Income Tax Reconciliation, Foreign Income Tax Rate Differential									(12,496)	(16,840)	(14,066)
Income Tax Reconciliation, Nondeductible Expense									7,006	2,936	2,832
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance									(1,744)	(899)	3,625
Income Tax Reconciliation, State and Local Income Taxes									829	600	1,133
Income Tax Reconciliation, Prior Year Income Taxes									(4,272)	2,412	483
Income Tax Reconciliation, Other Adjustments									1,869	(604)	(1,205)
Income Tax Reconciliation, Foreign Exchange									(1,792)	3,381	4,358
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Amount									3,067	246	(247)
Income Tax Reconciliation, Other Reconciling Items									716	864	(328)
Income Tax Expense (Benefit)	$ 8,009	$ 3,716	$ 4,006	$ 2,879	$ 3,607	$ 2,081	$ 671	$ 4,389	$ 18,610	$ 10,748	$ 33,758