Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 117,844	$ 93,131	$ 335,665	$ 263,625
Less: Preferred stock dividends	2,016	2,016	6,047	6,047
Net income available to common shareholders	115,828	91,115	329,618	257,578
Less: Earnings allocated to participating securities	750	475	2,178	1,346
Distributed earnings allocated to common stock	42,811	36,174	121,907	107,194
Undistributed earnings allocated to common stock	72,267	54,466	205,533	149,038
Net earnings allocated to common stock	$ 115,078	$ 90,640	$ 327,440	$ 256,232
Weighted-average shares outstanding for basic earnings per common share	63,892,023	63,667,356	63,793,514	63,822,011
Dilutive effect of stock compensation	1,022,168	897,945	1,037,043	957,337
Weighted-average shares outstanding for diluted earnings per common share	64,914,191	64,565,301	64,830,557	64,779,348