Earnings Per Share (Computation Of Basic And Diluted Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 79,657	$ 91,948	$ 89,580	$ 81,981	$ 68,781	$ 65,626	$ 64,897	$ 58,378	$ 343,166	$ 257,682	$ 206,875
Less: Preferred stock dividends	2,050	2,050	2,050	2,050	2,050	2,050	2,050	3,628	8,200	9,778	14,513
Net income applicable to common shares	$ 77,607	$ 89,898	$ 87,530	$ 79,931	$ 66,731	$ 63,576	$ 62,847	$ 54,750	334,966	247,904	192,362
Add: Dividends on convertible preferred stock, if dilutive									0	1,578	6,313
Net income applicable to common shares—Diluted									$ 334,966	$ 249,482	$ 198,675
Weighted average common shares outstanding (in shares)									56,300	54,703	50,278
Common stock equivalents (in shares)									908	998	894
Convertible preferred stock, if dilutive (in shares)									0	985	3,100
Total dilutive potential common shares (in shares)									908	1,983	3,994
Weighted average common shares and effect of dilutive potential common shares (in shares)									57,208	56,686	54,272
Net income per common share:
Basic (usd per share)	$ 1.38	$ 1.59	$ 1.55	$ 1.42	$ 1.19	$ 1.14	$ 1.15	$ 1.05	$ 5.95	$ 4.53	$ 3.83
Diluted (usd per share)	$ 1.35	$ 1.57	$ 1.53	$ 1.40	$ 1.17	$ 1.12	$ 1.11	$ 1.00	$ 5.86	$ 4.40	$ 3.66