Earnings Per Share (Comparison Of Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basic earnings per share:
Net income	$ 130,509	$ 30,915	$ 151,863	$ 176,972	$ 137,907	$ 122,843	$ (1,862)	$ 158,992	$ 490,259	$ 417,880	$ 493,007
Weighted average common shares outstanding	96,386,796	96,458,231	97,809,639	99,545,187	100,814,955	101,974,077	103,267,659	103,840,818	97,538,319	102,464,715	108,171,435
Basic earnings per share	$ 1.35	$ 0.32	$ 1.55	$ 1.78	$ 1.37	$ 1.20	$ (0.02)	$ 1.53	$ 5.03	$ 4.08	$ 4.56
Diluted earnings per share:
Net income	$ 130,509	$ 30,915	$ 151,863	$ 176,972	$ 137,907	$ 122,843	$ (1,862)	$ 158,992	$ 490,259	$ 417,880	$ 493,007
Weighted average common shares outstanding	96,386,796	96,458,231	97,809,639	99,545,187	100,814,955	101,974,077	103,267,659	103,840,818	97,538,319	102,464,715	108,171,435
Share equivalents:
Warrants and options									1,432,960	1,536,939	1,306,002
RSUs and LTIP awards									605,808	864,180	1,727,265
Employee share purchase plan									14,686	0	4,953
Weighted average common shares and common share equivalents outstanding - diluted	98,394,432	98,444,238	99,724,802	101,584,662	103,129,812	104,184,579	103,267,659	106,295,529	99,591,773	104,865,834	111,209,655
Diluted earnings per share	$ 1.33	$ 0.31	$ 1.52	$ 1.74	$ 1.34	$ 1.18	$ (0.02)	$ 1.50	$ 4.92	$ 3.98	$ 4.43