Segment Information (Financial Information) (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 Statement [Abstract]
Operating revenue	$ 454,157	$ 483,131	$ 473,978	$ 439,851	$ 474,914	$ 523,896	$ 500,204	$ 453,543	$ 1,851,117	$ 1,952,557	$ 1,528,110
Depreciation and amortization									177,806	172,578	150,377
Operating Income/(Loss)	65,366	62,296	78,393	32,563	57,596	85,721	76,398	58,225	238,618	277,940	203,449
Equity in (losses)/earnings of affiliates, net of tax	46	$ (229)	$ (280)	$ (723)	(99)	$ 607	$ 78	$ (90)	(1,186)	496	13,720
Net income from continuing operations									149,534	109,946	129,552
Capital Expenditures									75,498	80,718	80,558
Statement of Financial Position [Abstract]
Investments in affiliates, net	38,989				40,809				38,989	40,809
Long-Lived Assets	3,647,145				3,515,647				3,647,145	3,515,647
Total assets	4,077,030				3,906,872				4,077,030	3,906,872
Domestic [Member]
Income Statement [Abstract]
Operating revenue									1,693,396	1,806,099	1,397,394
Statement of Financial Position [Abstract]
Total assets	3,317,910				3,198,197				3,317,910	3,198,197
Foreign [Member]
Income Statement [Abstract]
Operating revenue									157,721	146,458	130,716
Statement of Financial Position [Abstract]
Total assets	329,235				317,450				329,235	317,450
Operating Segments [Member] | PIRM Segment [Member]
Income Statement [Abstract]
Operating revenue									703,032	706,496	712,335
Depreciation and amortization									99,558	101,196	101,422
Operating Income/(Loss)									89,129	101,700	96,707
Equity in (losses)/earnings of affiliates, net of tax									(420)	(1,432)	(1,569)
Net income from continuing operations									86,988	105,349	94,558
Capital Expenditures									56,157	53,217	56,467
Statement of Financial Position [Abstract]
Investments in affiliates, net	31,691				27,218				31,691	27,218
Long-Lived Assets	1,721,815				1,691,836				1,721,815	1,691,836
Total assets	1,911,222				1,842,361				1,911,222	1,842,361
Operating Segments [Member] | PIRM Segment [Member] | Domestic [Member]
Income Statement [Abstract]
Operating revenue									545,311	560,085	584,396
Statement of Financial Position [Abstract]
Long-Lived Assets	1,392,580				1,374,390				1,392,580	1,374,390
Operating Segments [Member] | PIRM Segment [Member] | Foreign [Member]
Income Statement [Abstract]
Operating revenue									157,721	146,411	127,939
Statement of Financial Position [Abstract]
Long-Lived Assets	329,235				317,446				329,235	317,446
Operating Segments [Member] | UWS Segment [Member]
Income Statement [Abstract]
Operating revenue									1,157,432	1,256,841	825,339
Depreciation and amortization									57,397	53,823	32,837
Operating Income/(Loss)									233,366	255,583	192,367
Equity in (losses)/earnings of affiliates, net of tax									(1,258)	3,020	24,191
Net income from continuing operations									222,928	237,767	216,111
Capital Expenditures									7,569	8,951	5,149
Statement of Financial Position [Abstract]
Investments in affiliates, net	4,552				8,592				4,552	8,592
Long-Lived Assets	1,996,417				1,738,627				1,996,417	1,738,627
Total assets	2,151,092				1,914,814				2,151,092	1,914,814
Operating Segments [Member] | UWS Segment [Member] | Domestic [Member]
Income Statement [Abstract]
Operating revenue									1,157,432	1,256,806	822,601
Statement of Financial Position [Abstract]
Long-Lived Assets	1,996,417				1,738,627				1,996,417	1,738,627
Operating Segments [Member] | UWS Segment [Member] | Foreign [Member]
Income Statement [Abstract]
Operating revenue									0	35	2,738
Statement of Financial Position [Abstract]
Long-Lived Assets	0				0				0	0
Corporate [Member]
Income Statement [Abstract]
Operating revenue									0	12	39
Depreciation and amortization									20,851	17,559	16,118
Operating Income/(Loss)									(83,877)	(79,343)	(85,625)
Equity in (losses)/earnings of affiliates, net of tax									492	(1,092)	(8,902)
Net income from continuing operations									(160,382)	(233,170)	(181,117)
Capital Expenditures									11,772	18,550	18,942
Statement of Financial Position [Abstract]
Investments in affiliates, net	2,746				4,999				2,746	4,999
Long-Lived Assets	5,542,323				5,510,684				5,542,323	5,510,684
Total assets	5,628,824				5,575,846				5,628,824	5,575,846
Corporate [Member] | Domestic [Member]
Income Statement [Abstract]
Operating revenue									0	0	0
Statement of Financial Position [Abstract]
Long-Lived Assets	4,796,378				4,764,740				4,796,378	4,764,740
Corporate [Member] | Foreign [Member]
Income Statement [Abstract]
Operating revenue									0	12	39
Statement of Financial Position [Abstract]
Long-Lived Assets	745,945				745,944				745,945	745,944
Eliminations [Member]
Income Statement [Abstract]
Operating revenue									(9,347)	(10,792)	(9,603)
Depreciation and amortization									0	0	0
Operating Income/(Loss)									0	0	0
Equity in (losses)/earnings of affiliates, net of tax									0	0	0
Net income from continuing operations									0	0	0
Capital Expenditures									0	0	0
Statement of Financial Position [Abstract]
Investments in affiliates, net	0				0				0	0
Long-Lived Assets	(5,613,410)				(5,425,500)				(5,613,410)	(5,425,500)
Total assets	(5,614,108)				(5,426,149)				(5,614,108)	(5,426,149)
Eliminations [Member] | Domestic [Member]
Income Statement [Abstract]
Operating revenue									(9,347)	(10,792)	(9,603)
Statement of Financial Position [Abstract]
Long-Lived Assets	(4,867,465)				(4,679,560)				(4,867,465)	(4,679,560)
Eliminations [Member] | Foreign [Member]
Income Statement [Abstract]
Operating revenue									0	0	$ 0
Statement of Financial Position [Abstract]
Long-Lived Assets	$ (745,945)				$ (745,940)				$ (745,945)	$ (745,940)