Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 111,341	$ 85,553	$ 217,821	$ 170,494
Less: Preferred stock dividends	2,015	2,015	4,031	4,031
Net income available to common shareholders	109,326	83,538	213,790	166,463
Less: Earnings allocated to participating securities	726	436	1,431	871
Distributed earnings allocated to common stock	42,791	36,545	79,096	71,020
Undistributed earnings allocated to common stock	65,809	46,557	133,263	94,572
Net earnings allocated to common stock	$ 108,600	$ 83,102	$ 212,359	$ 165,592
Weighted-average shares outstanding for basic earnings per common share	63,836,651	64,061,264	63,743,442	63,900,620
Dilutive effect of stock compensation	1,062,637	974,067	1,043,712	988,198
Weighted-average shares outstanding for diluted earnings per common share	64,899,288	65,035,331	64,787,154	64,888,818