Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 68,779	$ 72,163
Less: Preferred stock dividends	2,016	2,016
Net income available to common shareholders	66,763	70,147
Less: Earnings allocated to participating securities	235	237
Distributed earnings allocated to common stock	32,822	32,179
Undistributed earnings allocated to common stock	33,706	37,731
Net earnings allocated to common stock	$ 66,528	$ 69,910
Weighted-average shares outstanding for basic earnings per common share	61,929,466	63,094,391
Dilutive effect of stock compensation	149,728	685,043
Weighted-average shares outstanding for diluted earnings per common share	62,079,194	63,779,434