Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 114,200	$ 128,798		$ 355,392		$ 378,263
Less: Dividends paid on and earnings allocated to participating securities	(723)	(1,213)		(2,248)		(3,552)
Earnings applicable to common stock	$ 113,477	$ 127,585		$ 353,144		$ 374,711
Weighted average common shares outstanding	439,435,579	437,787,688		439,199,487		437,692,411
Basic earnings per common share	$ 0.26	$ 0.29		$ 0.80		$ 0.86
Potential dilutive common shares		5,664	[1]	3,971	[1]	5,026	[1]
Total shares for diluted earnings per share computation	439,435,579	437,793,352		439,203,458		437,697,437
Diluted earnings per common share and common share equivalents	$ 0.26	$ 0.29		$ 0.80		$ 0.86

[1] 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 would have had an antidilutive effect. Options to purchase 2,579,585 shares of the Company's common stock that were outstanding in the three and nine months ended September 30, 2012, at a weighted average exercise price of $16.86, were excluded from the respective computations of diluted EPS because their inclusion also would have had an antidilutive effect.