Net Income (Loss) Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Numerator [Abstract]
Net income (loss)	$ 176,146	$ 124,185	$ 536,287	$ (682,771)
Dividends on preferred shares	(15,405)	(8,631)	(30,811)	(17,263)
Net income (loss) available to common shareholders	$ 160,741	$ 115,554	$ 505,476	$ (700,034)
Denominator [Abstract]
Weighted Average Number Of Shares Outstanding Basic	63,816,027	67,628,052	64,610,127	67,811,366
Share options and other	607,000	814,200	522,800	0
Weighted average number of common shares and common share equivalents outstanding	64,423,036	68,442,300	65,132,928	67,811,366
Basic net income (loss)	$ 2.52	$ 1.71	$ 7.82	$ (10.32)
Diluted net income (loss)	$ 2.50	$ 1.69	$ 7.76	$ (10.32)
Share options excluded from computation of weighted average number of common share and common share equivalents outstanding	1,512,600	1,253,600
Weighted Average Number Of Potentially Dilutive Common Shares And Common Share Equivalents Outstanding				958,500