Goodwill and Other Intangible Assets (Schedule of intangible assets subject to amortization) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	$ 254,459	$ 304,192
Intangible assets acquired during the year	3,175	0
Amortization during the year	(34,279)	(39,545)	$ (29,909)
Currency translation during the year	24,204	(10,188)
Intangible assets subject to amortization, ending balance	247,559	254,459	304,192
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	235,704	271,123
Intangible assets acquired during the year	3,175	0
Amortization during the year	(26,602)	(25,778)
Currency translation during the year	22,558	(9,641)
Intangible assets subject to amortization, ending balance	234,835	235,704	271,123
Patents
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	13,424	26,985
Intangible assets acquired during the year	0	0
Amortization during the year	(7,543)	(13,141)
Currency translation during the year	1,180	(420)
Intangible assets subject to amortization, ending balance	7,061	13,424	26,985
Other
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	5,331	6,084
Intangible assets acquired during the year	0	0
Amortization during the year	(134)	(626)
Currency translation during the year	466	(127)
Intangible assets subject to amortization, ending balance	$ 5,663	$ 5,331	$ 6,084