Net Income Per Share (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Numerator [Abstract]
Net (loss) income	$ (17,600,000)	$ 180,100,000	$ 124,200,000	$ (807,000,000)	$ 57,000,000	$ 524,900,000	$ 190,900,000	$ 79,600,000	$ (520,291,000)	$ 852,552,000	$ 1,536,854,000
Dividends on preferred shares	(15,400,000)	(14,400,000)	(8,600,000)	(8,600,000)	(8,600,000)	(8,600,000)	(8,600,000)	(8,600,000)	(47,020,000)	(34,525,000)	(34,525,000)
Net (loss) income available to common shareholders	(33,000,000)	165,700,000	115,600,000	(815,600,000)	48,400,000	516,300,000	182,300,000	71,000,000	(567,311,000)	818,027,000	1,502,329,000
Denominator [Abstract]
Weighted average number of common shares outstanding									67,558,732	76,839,519	62,786,234
Share options and other									0	1,394,800	1,104,400
Weighted average number of common shares and common share equivalents outstanding									67,558,732	78,234,312	63,890,638
Basic net (loss) income	$ (0.49)	$ 2.45	$ 1.71	$ (11.99)	$ 0.66	$ 6.86	$ 2.36	$ 0.87	$ (8.40)	$ 10.65	$ 23.93
Diluted net (loss) income	$ (0.49)	$ 2.43	$ 1.69	$ (11.99)	$ 0.65	$ 6.76	$ 2.31	$ 0.85	$ (8.40)	$ 10.46	$ 23.51
Notes to Net Income Per Share [Abstract]
Share options excluded from computation of weighted average number of common share and common share equivalents outstanding									2,854,400	489,700	387,000
Amount of net income attributable to non-controlling interest of subsidiary for the period October 2, 2009 to December 7, 2009											$ 4,300,000
Diluted net income per share attributable to non-controlling interest of subsidiary for the period October 2, 2009 to December 7, 2009											$ 0.07
Weighted average number of potentially dilutive common shares and common share equivalents outstanding									687,300