Earnings Per Common Share (Basic and Diluted Earnings Per Common Share) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 304,261	$ 279,328	$ 277,977
Less: Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	296,198	271,265	269,914
Less: Earnings allocated to participating securities	1,145	941	1,001
Distributed earnings allocated to common stock	134,374	131,702	126,709
Undistributed earnings allocated to common stock	160,679	138,622	142,204
Net earnings allocated to common stock	$ 295,053	$ 270,324	$ 268,913
Weighted-average shares outstanding for basic earnings per common share	62,376,260	62,758,074	62,072,080
Dilutive effect of stock compensation	592,615	715,250	901,448
Weighted-average shares outstanding for diluted earnings per common share	62,968,875	63,473,324	62,973,528