Computation of Basic and Diluted EPS (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income available to common shareholders	$ 99,147	$ 107,048	$ 197,492	$ 211,005
Less: Dividends paid on and earnings allocated to participating securities	(1,267)	(873)	(2,524)	(1,693)
Earnings applicable to common stock	$ 97,880	$ 106,175	$ 194,968	$ 209,312
Weighted average common shares outstanding	488,530,527	487,282,404	488,336,395	486,899,209
Basic earnings per common share	$ 0.20	$ 0.22	$ 0.40	$ 0.43
Potential dilutive common shares	0	0	0	0
Total shares for diluted earnings per share computation	488,530,527	487,282,404	488,336,395	486,899,209
Diluted earnings per common share and common share equivalents	$ 0.20	$ 0.22	$ 0.40	$ 0.43