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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share Reconciliation [Abstract]
Net income	$ 69,893	$ 64,496	$ 61,579	$ 59,471	$ 57,660	$ 51,817	$ 50,603	$ 47,047	$ 255,439	$ 207,127	$ 204,729
Less: Preferred stock dividends									8,184	8,096	8,711
Net income available to common shareholders, basic		$ 62,426	$ 59,485	$ 57,342	$ 55,501	$ 49,634	$ 48,398	$ 44,921	247,255	199,031	196,018
Net income available to common shareholders, diluted									247,255	199,031	196,018
Less: Earnings applicable to participating securities, basic									424	608	657
Less: Earnings applicable to participating securities, diluted									424	608	657
Earnings applicable to common shareholders	$ 67,710								246,831	198,423	195,361
Earnings applicable to common shareholders, diluted									$ 246,831	$ 198,423	$ 195,361
Shares:
Weighted-average common shares outstanding - basic									91,965	91,367	90,968
Effect of dilutive securities:
Stock options and restricted stock (in shares)									385	461	524
Warrants (in shares)									6	28	41
Weighted Average Number of Shares Outstanding, Diluted									92,356	91,856	91,533
Earnings per common share:
Earnings per common share, Basic (in dollars per share)	$ 0.74	$ 0.68	$ 0.65	$ 0.62	$ 0.61	$ 0.54	$ 0.53	$ 0.49	$ 2.68	$ 2.17	$ 2.15
Earnings per common share, Diluted (in dollars per share)	$ 0.73	$ 0.67	$ 0.64	$ 0.62	$ 0.60	$ 0.54	$ 0.53	$ 0.49	$ 2.67	$ 2.16	$ 2.13