Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income		$ 125,299	$ 114,688	$ 381,668	$ 357,651
Less: Dividends paid on and earnings allocated to participating securities		(973)	(834)	(2,928)	(2,594)
Earnings applicable to common stock		$ 124,326	$ 113,854	$ 378,740	$ 355,057
Weighted average common shares outstanding		485,352,998	442,707,699	485,087,197	442,475,699
Basic earnings per common share		$ 0.26	$ 0.26	$ 0.78	$ 0.80
Potential dilutive common shares	[1]	0	0	0	0
Total shares for diluted earnings per share computation		485,352,998	442,707,699	485,087,197	442,475,699
Diluted earnings per common share and common share equivalents		$ 0.26	$ 0.26	$ 0.78	$ 0.80

[1] At September 30, 2016, there were no stock options outstanding.