Interim Financial Information (Unaudited) (Schedule of Quarterly Financial Information) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Revenues, Net	$ 435,247	$ 395,328	$ 379,322	$ 381,961	$ 366,712	$ 332,056	$ 327,570	$ 326,239	$ 1,591,858	$ 1,352,577	$ 1,187,741
Operating Expenses	(350,275)	(272,941)	(131,998)	(254,477)	(286,048)	(245,197)	(229,294)	(229,200)	(1,009,691)	(989,739)	(861,225)
Operating Income	84,972	122,387	247,324	127,484	80,664	86,859	98,276	97,039	582,167	362,838	326,516
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	34,962	57,950	135,731	61,517	15,191	36,543	41,405	43,077	290,160	136,216	126,362
Income from discontinued operations, net of income taxes					0	105	105	104	0	314	92
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	34,962	57,950	135,731	61,517					290,160	136,530	126,454
Net Income	$ 35,379	$ 58,111	$ 135,731	$ 61,517	$ 15,191	$ 36,648	$ 41,510	$ 43,181	$ 290,738	$ 136,530	$ 126,454
Earnings Per Share, Basic [Abstract]
Income From Continuing Operations	$ 0.49	$ 0.81	$ 1.90	$ 0.86	$ 0.22	$ 0.52	$ 0.59	$ 0.62	$ 4.06	$ 1.94	$ 1.82
Income From Discontinued Operations					$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Net Income	$ 0.49	$ 0.81	$ 1.90	$ 0.86	$ 0.22	$ 0.52	$ 0.59	$ 0.62	$ 4.06	$ 1.94	$ 1.83
Earnings Per Share, Diluted [Abstract]
Income From Continuing Operations	$ 0.49	$ 0.80	$ 1.87	$ 0.85	$ 0.21	$ 0.51	$ 0.57	$ 0.60	$ 4.00	$ 1.89	$ 1.79
Income From Discontinued Operations					$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Net Income	$ 0.49	$ 0.80	$ 1.87	$ 0.85	$ 0.21	$ 0.51	$ 0.58	$ 0.60	$ 4.00	$ 1.89	$ 1.79