Computation of Basic and Diluted Earnings Per Share (Detail) (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
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 122,517		$ 131,212		$ 241,192		$ 249,465
Less: Dividends paid on and earnings allocated to participating securities	(791)		(1,246)		(1,525)		(2,339)
Earnings applicable to common stock	$ 121,726		$ 129,966		$ 239,667		$ 247,126
Weighted average common shares outstanding	439,452,048		437,820,639		439,079,827		437,644,249
Basic earnings per common share	$ 0.28		$ 0.30		$ 0.55		$ 0.56
Potential dilutive common shares	3,298	[1]	4,063	[1]	3,445	[1]	4,698	[1]
Total shares for diluted earnings per share computation	439,455,346		437,824,702		439,083,272		437,648,947
Diluted earnings per common share and common share equivalents	$ 0.28		$ 0.30		$ 0.55		$ 0.56

[1] Options to purchase 253,500 shares of the Company's common stock that were outstanding in the three and six months ended June 30, 2013, at a weighted average exercise price of $22.14, were excluded from the respective computations of diluted EPS because their inclusion would have had an antidilutive effect. Options to purchase 4,981,879 shares of the Company's common stock that were outstanding in the three and six months ended June 30, 2012, at a weighted average exercise price of $15.40, were excluded from the respective computations of diluted EPS because their inclusion also would have had an antidilutive effect.