Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$ 127,515		$ 107,704
Number of common shares, Weighted average outstanding	350,032,430		348,000,074
Number of common shares, Issued upon assumed exercise of outstanding stock options	579,022		1,889,691
Number of common shares, Effect of issuance of nonvested restricted common stock	126,857		100,960
Number of common shares, Weighted average and potential dilutive outstanding	350,738,309	[1]	349,990,725	[1]
Basic	$ 0.36		$ 0.31
Diluted	$ 0.36		$ 0.31
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2,112,679		1,702,166
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	271,674		657,763
Parent [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$ 127,515		$ 107,704

[1] Options for 2,112,679 shares and 271,674 shares of restricted stock were excluded from the calculation for the three months ended March 31, 2013 because they would have had an antidilutive effect. Options for 1,702,166 shares and 657,763 shares of restricted stock were excluded from the calculation for the three months ended March 31, 2012 because they would have had an antidilutive effect.