Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
		Jun. 30, 2018	Jun. 30, 2018
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance			$ 852,301
Other comprehensive income before reclassifications		$ (36,688)	(12,832)
Amounts reclassified from OCI		42	50
Ending balance		816,429	816,429
Accumulated Other Comprehensive (Loss) Income [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(125,470)	(149,334)
Ending balance		(162,116)	(162,116)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance	[1]	39	(669)
Other comprehensive income before reclassifications	[1]	(145)	525
Amounts reclassified from OCI	[1]	72	110
Ending balance	[1]	(34)	(34)
Pension Items [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance	[1]	(339)	(309)
Other comprehensive income before reclassifications	[1]	0	0
Amounts reclassified from OCI	[1]	(30)	(60)
Ending balance	[1]	(369)	(369)
Foreign Currency Items [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(125,170)	(148,356)
Other comprehensive income before reclassifications		(36,543)	(13,357)
Amounts reclassified from OCI		0	0
Ending balance		$ (161,713)	$ (161,713)

[1] Cash Flow Hedges and Pension Items are net of tax.