Computation of Earnings per Share - Computation of Basic and Diluted Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 120,258	$ 114,200	$ 354,200	$ 355,392
Less: Dividends paid on and earnings allocated to participating securities	(851)	(723)	(2,500)	(2,248)
Earnings applicable to common stock	$ 119,407	$ 113,477	$ 351,700	$ 353,144
Weighted average common shares outstanding	441,127,550	439,435,579	440,953,121	439,199,487
Basic earnings per common share	$ 0.27	$ 0.26	$ 0.80	$ 0.80
Potential dilutive common shares				3,971	[1]
Total shares for diluted earnings per share computation	441,127,550	439,435,579	440,953,121	439,203,458
Diluted earnings per common share and common share equivalents	$ 0.27	$ 0.26	$ 0.80	$ 0.80

[1] Options to purchase 58,560 shares of the Company’s common stock that were outstanding in the three and nine months ended September 30, 2014, at a weighted average exercise price of $18.04, were excluded from the respective computations of diluted EPS because their inclusion would have had an antidilutive effect. Options to purchase 62,040 shares of the Company’s common stock that were outstanding in the three and nine months ended September 30, 2013, at a weighted average exercise price of $17.95, were excluded from the respective computations of diluted EPS because their inclusion also would have had an antidilutive effect.