Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 66,470	$ 59,663	$ 127,658	$ 114,851
Less: Preferred stock dividends	2,015	2,688	4,031	2,688
Net income available to common shareholders	64,455	56,975	123,627	112,163
Less: Earnings allocated to participating securities	246	209	472	407
Net earnings allocated to common stock	64,209	56,766	123,155	111,756
Distributed earnings allocated to common stock	32,050	30,058	62,421	58,733
Undistributed earnings allocated to common stock	32,159	26,708	60,734	53,023
Net earnings allocated to common stock	$ 64,209	$ 56,766	$ 123,155	$ 111,756
Weighted-average shares outstanding for basic earnings per common share	61,551,473	60,010,527	61,128,725	60,299,939
Dilutive effect of stock compensation	915,083	664,597	902,024	628,961
Weighted-average shares outstanding for diluted earnings per common share	62,466,556	60,675,124	62,030,749	60,928,900