Shareholders' Equity And Earnings Per Share (Computation Of Basic And Diluted Earnings Per Common Share) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Net income	$ 99,121	$ 91,948	$ 269,733	$ 263,509
Less: Preferred stock dividends	2,050	2,050	6,150	6,150
Net income applicable to common shares	$ 97,071	$ 89,898	$ 263,583	$ 257,359
Weighted average common shares outstanding (in shares)	56,690	56,366	56,627	56,268
Effect of dilutive potential common shares
Common stock equivalents (in shares)	773	918	724	912
Average common shares and dilutive common shares (in shares)	57,463	57,284	57,351	57,180
Net income per common share:
Basic (usd per share)	$ 1.71	$ 1.59	$ 4.65	$ 4.57
Diluted (usd per share)	$ 1.69	$ 1.57	$ 4.60	$ 4.50