Earnings Per Common Share (Earnings Per Share Basic And Diluted) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 52,579	$ 51,536	$ 52,503	$ 49,722	$ 51,006	$ 50,457	$ 47,834	$ 50,429	$ 206,340	$ 199,726	$ 179,456
Less: Preferred stock dividends									(8,711)	(10,556)	(10,803)
Net income available to common shareholders	$ 50,414	$ 49,341	$ 50,277	$ 46,937	$ 48,224	$ 47,647	$ 45,008	$ 47,617	197,629	189,170	168,653
Less: Earnings applicable to participating securities									660	674	617
Earnings applicable to common shareholders									196,969	188,496	168,036
Net income									206,340	199,726	179,456
Net income available to common shareholders									197,629	189,170	168,653
Less: Earnings applicable to participating securities									660	674	617
Earnings applicable to common shareholders									$ 196,969	$ 188,496	$ 168,036
Weighted-average common shares outstanding - basic									90,968	89,899	88,713
Stock options and restricted stock (in shares)									524	466	436
Weighted-average common shares outstanding - diluted									91,533	90,620	90,261
Earnings per common share, Basic (in dollars per share)	$ 0.55	$ 0.54	$ 0.55	$ 0.52	$ 0.54	$ 0.53	$ 0.50	$ 0.53	$ 2.17	$ 2.10	$ 1.90
Earnings per common share, Diluted (in dollars per share)	$ 0.55	$ 0.54	$ 0.55	$ 0.52	$ 0.53	$ 0.53	$ 0.50	$ 0.53	$ 2.15	$ 2.08	$ 1.86
Warrant - US Treasury [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Warrants (in shares)									41	255	190
Warrants - Warburg [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Warrants (in shares)									0	0	922