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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Net income	$ 91,948	$ 65,626	$ 263,509	$ 188,901
Less: Preferred stock dividends	2,050	2,050	6,150	7,728
Net income applicable to common shares	89,898	63,576	257,359	181,173
Add: Dividends on convertible preferred stock, if dilutive	0	0	0	1,578
Net income applicable to common shares—Diluted	$ 89,898	$ 63,576	$ 257,359	$ 182,751
Weighted average common shares outstanding (in shares)	56,366	55,796	56,268	54,292
Effect of dilutive potential common shares
Common stock equivalents (in shares)	918	966	912	988
Convertible preferred stock, if dilutive (in shares)	0	0	0	1,317
Total dilutive potential common shares (in shares)	918	966	912	2,305
Weighted average common shares and effect of dilutive potential common shares (in shares)	57,284	56,762	57,180	56,597
Net income per common share:
Basic (usd per share)	$ 1.59	$ 1.14	$ 4.57	$ 3.34
Diluted (usd per share)	$ 1.57	$ 1.12	$ 4.50	$ 3.23