Earnings Per Common Share (Basic and Diluted Earnings Per Common Share) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 279,328	$ 277,977	$ 237,866
Less: Preferred stock dividends	8,063	8,063	6,719
Net income available to common shareholders	271,265	269,914	231,147
Less: Earnings allocated to participating securities	941	1,001	850
Distributed earnings allocated to common stock	131,702	126,709	119,177
Undistributed earnings allocated to common stock	138,622	142,204	111,120
Net earnings allocated to common stock	$ 270,324	$ 268,913	$ 230,297
Weighted-average shares outstanding for basic earnings per common share	62,758,074	62,072,080	60,350,552
Dilutive effect of stock compensation	715,250	901,448	765,858
Weighted-average shares outstanding for diluted earnings per common share	63,473,324	62,973,528	61,116,410