Segment Information (Financial Information) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating Revenues	$ 488,401	$ 473,978	$ 933,301	$ 913,829
Depreciation and Amortization	47,396	42,871	93,536	86,343
Operating Income/(Loss)	89,637	78,393	134,056	110,958
Equity in Earnings/(Losses) of Affiliates, Net of Tax	2,837	(280)	3,070	(1,004)
Net Income/(Loss) From Continuing Operations	58,532	41,182	86,894	53,891
Capital Expenditures	20,483	20,327	39,967	37,439
Assets	4,156,327		4,156,327		$ 4,077,030
PIRM
Segment Reporting Information [Line Items]
Segment reporting intercompany revenue	1,700	1,600	3,200	3,000
Segment reporting intercompany expense	800	700	1,600	1,500
UWS
Segment Reporting Information [Line Items]
Segment reporting intercompany revenue	800	700	1,600	1,500
Segment reporting intercompany expense	1,700	1,600	3,200	3,000
Operating Segments | PIRM
Segment Reporting Information [Line Items]
Operating Revenues	182,655	176,311	356,422	342,067
Depreciation and Amortization	25,512	24,132	51,247	48,992
Operating Income/(Loss)	28,974	32,099	49,752	47,671
Equity in Earnings/(Losses) of Affiliates, Net of Tax	3,740	(166)	4,011	(459)
Net Income/(Loss) From Continuing Operations	32,295	31,470	52,966	46,231
Capital Expenditures	13,917	14,812	27,123	27,600
Assets	1,900,141		1,900,141		1,911,222
Operating Segments | UWS
Segment Reporting Information [Line Items]
Operating Revenues	308,226	300,031	581,645	576,222
Depreciation and Amortization	16,483	13,605	31,447	27,408
Operating Income/(Loss)	85,897	66,596	133,950	103,849
Equity in Earnings/(Losses) of Affiliates, Net of Tax	(10)	(174)	8	(967)
Net Income/(Loss) From Continuing Operations	85,868	60,470	133,622	96,664
Capital Expenditures	2,386	2,413	4,699	3,837
Assets	2,260,370		2,260,370		2,151,092
Corporate
Segment Reporting Information [Line Items]
Operating Revenues	0	0	0	0
Depreciation and Amortization	5,401	5,134	10,842	9,943
Operating Income/(Loss)	(25,234)	(20,302)	(49,646)	(40,562)
Equity in Earnings/(Losses) of Affiliates, Net of Tax	(893)	60	(949)	422
Net Income/(Loss) From Continuing Operations	(59,631)	(50,758)	(99,694)	(89,004)
Capital Expenditures	4,180	3,102	8,145	6,002
Assets	5,751,261		5,751,261		5,628,824
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	(2,480)	(2,364)	(4,766)	(4,460)
Depreciation and Amortization	0	0	0	0
Operating Income/(Loss)	0	0	0	0
Equity in Earnings/(Losses) of Affiliates, Net of Tax	0	0	0	0
Net Income/(Loss) From Continuing Operations	0	0	0	0
Capital Expenditures	0	$ 0	0	$ 0
Assets	$ (5,755,445)		$ (5,755,445)		$ (5,614,108)