Net Income (Loss) Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Numerator [Abstract]
Net income (loss)	$ 360,141	$ (806,956)
Dividends on preferred shares	(15,405)	(8,631)
Net income (loss) available to common shareholders	$ 344,736	$ (815,587)
Denominator [Abstract]
Weighted average number of common shares outstanding	65,404,227	67,997,426
Share options and other	438,600	0
Weighted average number of common shares and common share equivalents outstanding	65,842,819	67,997,426
Basic net income (loss)	$ 5.27	$ (11.99)
Diluted net income (loss)	$ 5.24	$ (11.99)
Share options excluded from computation of weighted average number of common share and common share equivalents outstanding	2,311,200	703,300
Weighted average number of potentially dilutive common shares and common share equivalents outstanding		1,102,700
Notes to net income per share
Weighted average number of common shares outstanding	65,404,227	67,997,426
Share options and other	438,600	0
Weighted average number of common shares and common share equivalents outstanding	65,842,819	67,997,426
Basic net income (loss)	$ 5.27	$ (11.99)
Diluted net income (loss)	$ 5.24	$ (11.99)
Share options excluded from computation of weighted average number of common share and common share equivalents outstanding	2,311,200	703,300
Weighted average number of potentially dilutive common shares and common share equivalents outstanding		1,102,700