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, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Share [Abstract]
Net income	$ 183,100	$ (10,972)	$ 93,800	$ 8,620	$ 92,786	$ 254,520	$ 183,959	$ 133,740	$ 274,548	$ 665,005	$ 606,887
Weighted average common shares outstanding	38,138,558	38,110,368	38,346,489	38,199,867	40,291,620	45,544,060	50,222,974	50,023,816	38,093,351	46,491,279	49,503,438
Basic earnings per share	$ 4.80	$ (0.29)	$ 2.45	$ 0.23	$ 2.30	$ 5.59	$ 3.66	$ 2.67	$ 7.21	$ 14.30	$ 12.26
Warrants and options									387,549	1,668,262	1,241,644
Restricted stock units									418,588	669,006	413,714
LTIP awards									767,176	1,084,389	833,878
Employee share repurchase plan									1,241	381
Weighted average common shares and common share equivalents outstanding - diluted	39,524,273	38,110,368	39,800,753	40,383,523	43,501,068	48,839,991	52,974,410	53,115,756	39,667,905	49,913,317	51,992,674
Diluted earnings per share	$ 4.63	$ (0.29)	$ 2.36	$ 0.21	$ 2.13	$ 5.21	$ 3.47	$ 2.52	$ 6.92	$ 13.32	$ 11.67