Net Income (Loss) Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Numerator [Abstract]
Net income (loss)	$ 124,185	$ 190,927	$ (682,771)	$ 270,581
Dividends on preferred shares	(8,631)	(8,631)	(17,263)	(17,263)
Net income (loss) available to common shareholders	$ 115,554	$ 182,296	$ (700,034)	$ 253,318
Denominator [Abstract]
Weighted average number of common shares outstanding	67,628,052	77,365,445	67,811,366	79,519,198
Share options and other	814,200	1,431,000	0	1,531,500
Weighted average number of common shares and common share equivalents outstanding	68,442,300	78,796,431	67,811,366	81,050,662
Basic net income (loss)	$ 1.71	$ 2.36	$ (10.32)	$ 3.19
Diluted net income (loss)	$ 1.69	$ 2.31	$ (10.32)	$ 3.13
Notes to Net Income (Loss) Per Share [Abstract]
Weighted average number of common shares and common share equivalents outstanding including potentially dilutive securities			68,769,900
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			1,253,600	840,400