Earnings Per Share (Computation Of Basic And Diluted Earnings Per Common Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 38,133	$ 40,224	$ 38,541	$ 34,500	$ 35,288	$ 35,563	$ 34,307	$ 32,052	$ 151,398	$ 137,210	$ 111,196
Less: Preferred stock dividends and discount accretion	1,580	1,581	1,581	1,581	1,581	1,581	2,617	2,616	6,323	8,395	9,093
Net income applicable to common shares - Basic	36,553	38,643	36,960	32,919	33,707	33,982	31,690	29,436	145,075	128,815	102,103
Add: Dividends on convertible preferred stock, if dilutive									6,323	8,325	8,955
Net income applicable to common shares - Diluted									$ 151,398	$ 137,140	$ 111,058
Weighted average common shares outstanding									46,524	38,699	36,365
Common stock equivalents (in shares)									1,246	7,108	7,313
Convertible preferred stock, if dilutive (in shares)									3,075	4,141	4,356
Total dilutive potential common shares (in shares)									4,321	11,249	11,669
Weighted average common shares and effect of dilutive potential common shares (in shares)									50,845	49,948	48,034
Net income per common share - Basic (in usd per share)	$ 0.78	$ 0.83	$ 0.79	$ 0.71	$ 0.82	$ 0.86	$ 0.85	$ 0.80	$ 3.12	$ 3.33	$ 2.81
Net income per common share - Diluted	$ 0.75	$ 0.79	$ 0.76	$ 0.68	$ 0.70	$ 0.71	$ 0.69	$ 0.65	$ 2.98	$ 2.75	$ 2.31