Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$ 207,000		$ 246,000		$ 401,000		$ 373,000
Number of common shares, Weighted average outstanding	351,391,582		350,448,806		351,307,527		350,241,768
Number of common shares, Issued upon assumed exercise of outstanding stock options	490,302		386,999		418,987		481,528
Diluted	352,579,522	[1],[2]	351,082,807	[1],[2]	352,306,268	[1],[2]	350,911,892	[1],[2]
Basic	$ 0.59		$ 0.70		$ 1.14		$ 1.07
Diluted	$ 0.59		$ 0.70		$ 1.14		$ 1.06
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	654,189		1,599,246		1,026,958		2,079,849
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of common shares, Effect of issuance of nonvested shares	577,599		247,002		472,008		188,596
Antidilutive securities excluded from computation of earnings per share, shares	19,045		29,251		22,952		246,347
Performance Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of common shares, Effect of issuance of nonvested shares	120,039				107,746

[1] Options for 654,189 shares and 19,045 shares of restricted stock were excluded from the calculation for the three months ended June 30, 2014 because they would have had an antidilutive effect. 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.

[2] Options for 1,026,958 shares and 22,952 shares of restricted stock were excluded from the calculation for the six months ended June 30, 2014 because they would have had an antidilutive effect. 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.