Computation of Basic and Diluted Earnings (Loss) Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income available to common shareholders	$ 389,589	$ 441,580	$ 495,401
Less: Dividends paid on and earnings allocated to participating securities	(4,871)	(3,554)	(3,795)
Earnings applicable to common stock	$ 384,718	$ 438,026	$ 491,606
Weighted average common shares outstanding	487,287,872	487,073,951	485,150,173
Basic earnings per common share	$ 0.79	$ 0.90	$ 1.01
Potential dilutive common shares	0	0	0
Total shares for diluted earnings per common share computation	487,287,872	487,073,951	485,150,173
Diluted earnings per common share and common share equivalents	$ 0.79	$ 0.90	$ 1.01