Goodwill and Other Intangible Assets (Schedule of Finite-Lived Intangible Assets by Major Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying value	$ 148,395	$ 148,395
Accumulated amortization and impairment losses	(93,924)	(82,937)
Other intangible assets, net	54,471	65,458
Licenses
Schedule of Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying value	10,267	10,267
Accumulated amortization and impairment losses	0	0
Other intangible assets, net	10,267	10,267
Customer relationships and customer lists
Schedule of Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying value	95,458	95,458
Accumulated amortization and impairment losses	(51,633)	(42,142)
Other intangible assets, net	43,825	53,316
Value of business acquired
Schedule of Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying value	20,200	20,200
Accumulated amortization and impairment losses	(20,200)	(19,527)
Other intangible assets, net	0	673
Software
Schedule of Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying value	12,230	12,230
Accumulated amortization and impairment losses	(12,230)	(11,938)
Other intangible assets, net	0	292
Patents and intellectual property
Schedule of Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying value	4,500	4,500
Accumulated amortization and impairment losses	(4,500)	(4,500)
Other intangible assets, net	0	0
Covenants not-to-compete
Schedule of Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying value	4,030	4,030
Accumulated amortization and impairment losses	(4,030)	(3,523)
Other intangible assets, net	0	507
Trademarks and trade names
Schedule of Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying value	1,710	1,710
Accumulated amortization and impairment losses	(1,331)	(1,307)
Other intangible assets, net	$ 379	$ 403