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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Net income	$ 89,580	$ 64,897	$ 171,561	$ 123,275
Less: Preferred stock dividends	2,050	2,050	4,100	5,678
Net income applicable to common shares	87,530	62,847	167,461	117,597
Add: Dividends on convertible preferred stock, if dilutive	0	0	0	1,578
Net income applicable to common shares—Diluted	$ 87,530	$ 62,847	$ 167,461	$ 119,175
Weighted average common shares outstanding (in shares)	56,299	54,775	56,218	53,528
Effect of dilutive potential common shares
Common stock equivalents (in shares)	928	927	909	994
Convertible preferred stock, if dilutive (in shares)	0	885	0	1,987
Total dilutive potential common shares (in shares)	928	1,812	909	2,981
Weighted average common shares and effect of dilutive potential common shares (in shares)	57,227	56,587	57,127	56,509
Net income per common share:
Basic (usd per share)	$ 1.55	$ 1.15	$ 2.98	$ 2.20
Diluted (usd per share)	$ 1.53	$ 1.11	$ 2.93	$ 2.11