Goodwill and Other Intangible Assets (Schedule of Goodwill and Other Intangible Assets Included in Equity Method Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other intangible assets
Gross amount	$ 148,395	$ 148,395
Accumulated impairment losses and amortization	(93,924)	(82,937)
Intangible Assets, Net, Excluding Goodwill [Roll Forward]
Other intangible assets, net, beginning balance	65,458
Other intangible assets, net, ending balance	54,471	65,458
Intangible Assets, Net, Including Goodwill [Roll Forward]
Goodwill and Other intangible assets, net, beginning balance	251,186
Goodwill and Other intangible assets, net, ending balance	243,145	251,186
Investments in other ventures, under equity method
Goodwill
Goodwill, gross amount	12,318	12,318	$ 12,318
Accumulated impairment losses and amortization	(4,500)	(4,500)	(4,500)
Goodwill	7,818	7,818	7,818
Other intangible assets
Gross amount	51,796	51,796	51,796
Accumulated impairment losses and amortization	(42,880)	(39,934)	(36,460)
Intangible Assets, Net, Excluding Goodwill [Roll Forward]
Other intangible assets, net, beginning balance	11,862	15,336
Amortization	(2,946)	(3,474)
Other intangible assets, net, ending balance	8,916	11,862
Goodwill and Other intangible assets, Total
Gross amount	64,114	64,114	64,114
Accumulated impairment losses and amortization	(47,380)	(44,434)	$ (40,960)
Intangible Assets, Net, Including Goodwill [Roll Forward]
Goodwill and Other intangible assets, net, beginning balance	19,680	23,154
Amortization	(2,946)	(3,474)
Goodwill and Other intangible assets, net, ending balance	$ 16,734	$ 19,680