Earnings Per Common Share (Basic and Diluted Earnings Per Common Share) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 364,149	$ 304,261	$ 279,328
Less: Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	356,086	296,198	271,265
Less: Earnings allocated to participating securities	2,016	1,145	941
Distributed earnings allocated to common stock	143,356	134,374	131,702
Undistributed earnings allocated to common stock	210,714	160,679	138,622
Net earnings allocated to common stock	$ 354,070	$ 295,053	$ 270,324
Weighted-average shares outstanding for basic earnings per common share	63,693,927	62,376,260	62,758,074
Dilutive effect of stock compensation	968,161	592,615	715,250
Weighted-average shares outstanding for diluted earnings per common share	64,662,088	62,968,875	63,473,324