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, 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
Earnings Per Share, Basic [Abstract]
Net income	$ 137,907	$ 122,843	$ (1,862)	$ 158,992	$ (41,147)	$ 219,647	$ 96,351	$ 218,156	$ 417,880	$ 493,007	$ 274,548
Weighted average common shares outstanding	33,604,985	33,991,359	34,422,553	34,613,606	35,097,043	35,652,768	36,288,596	37,205,166	34,154,905	36,057,145	38,093,351
Basic earnings per share	$ 4.10	$ 3.61	$ (0.05)	$ 4.59	$ (1.17)	$ 6.16	$ 2.66	$ 5.86	$ 12.23	$ 13.67	$ 7.21
Earnings Per Share, Diluted [Abstract]
Net income	$ 137,907	$ 122,843	$ (1,862)	$ 158,992	$ (41,147)	$ 219,647	$ 96,351	$ 218,156	$ 417,880	$ 493,007	$ 274,548
Weighted average common shares outstanding	33,604,985	33,991,359	34,422,553	34,613,606	35,097,043	35,652,768	36,288,596	37,205,166	34,154,905	36,057,145	38,093,351
Share equivalents:
Warrants and options									512,313	435,334	387,549
RSUs and LTIP awards									288,060	575,755	1,185,764
Employee share purchase plan									0	1,651	1,241
Weighted average common shares and common share equivalents outstanding - diluted	34,376,604	34,728,193	34,422,553	35,431,843	35,097,043	36,616,734	37,189,722	38,284,635	34,955,278	37,069,885	39,667,905
Diluted earnings per share	$ 4.01	$ 3.54	$ (0.05)	$ 4.49	$ (1.17)	$ 6.00	$ 2.59	$ 5.70	$ 11.95	$ 13.30	$ 6.92