Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss)	$ 245,631		$ (405,132)		$ 373,146		$ (297,428)
Number of common shares, Weighted average outstanding	350,448,806		348,162,723		350,241,768		348,081,399
Number of common shares, Issued upon assumed exercise of outstanding stock options	386,999				481,528
Number of common shares, Effect of issuance of nonvested restricted common stock	247,002				188,596
Number of common shares, Weighted average and potential dilutive outstanding	351,082,807	[1]	348,162,723	[1]	350,911,892	[1]	348,081,399	[1]
Basic	$ 0.70		$ (1.16)		$ 1.07		$ (0.85)
Diluted	$ 0.70		$ (1.16)		$ 1.06		$ (0.85)
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	1,599,246		1,723,316		2,079,849		1,783,073
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	29,251		156,047		246,347		121,078
Parent [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss)	$ 245,631		$ (405,132)		$ 373,146		$ (297,428)

[1] Options for 1,599,246 shares and 29,251 shares of restricted stock were excluded from the calculation for the three months ended June 30, 2013 because they would have had an antidilutive effect. Due to the net loss for the three months ended June 30, 2012, options for 1,723,316 shares and 156,047 shares of restricted stock were antidilutive and excluded from the calculation. Options for 2,079,849 shares and 246,347 shares of restricted stock were excluded from the calculation for the six months ended June 30, 2013 because they would have had an antidilutive effect. Due to the net loss for the six months ended June 30, 2012, options for 1,783,073 shares and 121,078 shares of restricted stock were antidilutive and excluded from the calculation.