Net Income (Loss) Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Numerator [Abstract]
Net income (loss)	$ 180,123	$ 524,937	$ (502,648)	$ 795,518
Dividends on preferred shares	(14,352)	(8,631)	(31,614)	(25,894)
Net income (loss) available to common shareholders	$ 165,771	$ 516,306	$ (534,262)	$ 769,624
Denominator [Abstract]
Weighted average number of common shares outstanding	67,743,296	75,238,329	67,788,427	78,076,561
Share options and other	438,700	1,190,200	0	1,417,600
Weighted average number of common shares and common share equivalents outstanding	68,181,982	76,428,460	67,788,427	79,494,247
Basic net income (loss)	$ 2.45	$ 6.86	$ (7.88)	$ 9.86
Diluted net income (loss)	$ 2.43	$ 6.76	$ (7.88)	$ 9.68
Notes to Net Income (Loss) Per Share [Abstract]
Weighted average number of common shares and common share equivalents outstanding including potentially dilutive securities			68,573,600
Stock Compensation Plans [Member]
Notes to Net Income (Loss) Per Share [Abstract]
Share options excluded from computation of weighted average number of common share and common share equivalents outstanding			2,996,100	897,300