Quarterly Operating Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Gain (Loss) on Disposition of Business										$ 47,400
Total revenues	$ 404,597	$ 432,167	$ 419,447	$ 404,298	$ 393,020	$ 421,418	$ 397,764	$ 363,594	$ 1,660,509	1,575,796	$ 1,363,279
Operating Expenses	309,560	319,337	318,533	310,520	354,574	308,733	295,983	276,757	1,257,950	1,236,047	1,005,670
Income before income taxes	95,037	112,830	100,914	93,778	38,446	112,685	101,781	86,837	402,559	339,749	357,609
Net Income (Loss) Attributable to Parent	$ 57,935	$ 67,427	$ 61,005	$ 56,951	$ 24,395	$ 68,331	$ 61,755	$ 52,415	$ 243,318	$ 206,896	$ 217,112
Earnings Per Share, Basic	$ 0.0041	$ 0.0048	$ 0.0043	$ 0.0040	$ 0.0017	$ 0.0047	$ 0.0043	$ 0.0036	$ 1.72	$ 1.43	$ 1.50
Diluted (in dollars per share)	$ 0.0041	$ 0.0047	$ 0.0043	$ 0.0039	$ 0.0017	$ 0.0047	$ 0.0042	$ 0.0036	$ 1.70	$ 1.41	$ 1.48