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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic earnings (loss) per share:
Net income (loss)	$ (41,147)	$ 219,647	$ 96,351	$ 218,156	$ 183,100	$ (10,972)	$ 93,800	$ 8,620	$ 493,007	$ 274,548	$ 665,005
Weighted average common shares outstanding	35,097,043	35,652,768	36,288,596	37,205,166	38,138,558	38,110,368	38,346,489	38,199,867	36,057,145	38,093,351	46,491,279
Basic earnings (loss) per share	$ (1.17)	$ 6.16	$ 2.66	$ 5.86	$ 4.80	$ (0.29)	$ 2.45	$ 0.23	$ 13.67	$ 7.21	$ 14.30
Diluted earnings (loss) per share:
Net income (loss)	$ (41,147)	$ 219,647	$ 96,351	$ 218,156	$ 183,100	$ (10,972)	$ 93,800	$ 8,620	$ 493,007	$ 274,548	$ 665,005
Weighted average common shares outstanding	35,097,043	35,652,768	36,288,596	37,205,166	38,138,558	38,110,368	38,346,489	38,199,867	36,057,145	38,093,351	46,491,279
Warrants and options									435,334	387,549	1,668,262
RSUs and LTIP awards									575,755	1,185,764	1,753,395
Employee stock purchase plan									1,651	1,241	381
Weighted average common shares and common share equivalents outstanding - diluted	35,097,043	36,616,734	37,189,722	38,284,635	39,524,273	38,110,368	39,800,753	40,383,523	37,069,885	39,667,905	49,913,317
Diluted earnings per share	$ (1.17)	$ 6.00	$ 2.59	$ 5.70	$ 4.63	$ (0.29)	$ 2.36	$ 0.21	$ 13.30	$ 6.92	$ 13.32