Investment Securities (Summary Of Amount Of Gross Unrealized Losses For Debt Securities And Estimated Fair Value) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses		$ 13,602
Available-for-sale, Less than 12 months - Estimated fair value		1,326,690
Available-for-sale, 12 months or more - Gross unrealized losses		129,717
Available-for-sale, 12 months or more - Estimated fair value		699,056
Available-for-sale, Total - Gross unrealized losses		143,319
Available-for-sale, Total - Estimated fair value		2,025,746
Investment Securities Gross Unrealized Losses Less Than 12 Months	$ 11,182	14,182
Investment Securities Estimated Fair Value Less Than 12 Months	1,909,125	1,389,574
Investment Securities Gross Unrealized Losses 12 Months or More	10,114	170,303
Investment Securities Estimated Fair Value 12 Months or More	633,493	770,245
Investment Securities Gross Unrealized Losses Total	21,296	184,485
Investment Securities Estimated Fair Value Total	2,542,618	2,159,819
Municipal Securities [Member]
Investment [Line Items]
Held-to-maturity, Less than 12 months - Gross unrealized losses	901	527
Held-to-maturity, Less than 12 months - Estimated fair value	55,763	62,762
Held-to-maturity, 12 months or more - Gross unrealized losses	155	277
Held-to-maturity, 12 months or more - Estimated fair value	11,681	14,003
Held-to-maturity, Total - Gross unrealized losses	1,056	804
Held-to-maturity, Total - Estimated fair value	67,444	76,765
Available-for-sale, Less than 12 months - Gross unrealized losses	305	258
Available-for-sale, Less than 12 months - Estimated fair value	34,703	36,551
Available-for-sale, 12 months or more - Gross unrealized losses	54	687
Available-for-sale, 12 months or more - Estimated fair value	4,125	4,616
Available-for-sale, Total - Gross unrealized losses	359	945
Available-for-sale, Total - Estimated fair value	38,828	41,167
Available-for-sale Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	0
Available-for-sale, Less than 12 months - Estimated fair value	0
Agency Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	65	4,510
Available-for-sale, Less than 12 months - Estimated fair value	34,737	295,694
Available-for-sale, 12 months or more - Gross unrealized losses	513	3,833
Available-for-sale, 12 months or more - Estimated fair value	137,964	101,188
Available-for-sale, Total - Gross unrealized losses	578	8,343
Available-for-sale, Total - Estimated fair value	172,701	396,882
Agency Guaranteed Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	5,361	1,914
Available-for-sale, Less than 12 months - Estimated fair value	1,330,271	425,114
Available-for-sale, 12 months or more - Gross unrealized losses	258	191
Available-for-sale, 12 months or more - Estimated fair value	15,351	12,124
Available-for-sale, Total - Gross unrealized losses	5,619	2,105
Available-for-sale, Total - Estimated fair value	1,345,622	437,238
Small Business Administration Loan-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	4,550	5,869
Available-for-sale, Less than 12 months - Estimated fair value	453,651	495,817
Available-for-sale, 12 months or more - Gross unrealized losses	6,229	3,022
Available-for-sale, 12 months or more - Estimated fair value	452,275	175,523
Available-for-sale, Total - Gross unrealized losses	10,779	8,891
Available-for-sale, Total - Estimated fair value	905,926	671,340
Mutual Funds And Other [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses		1,044
Available-for-sale, Less than 12 months - Estimated fair value		71,907
Available-for-sale, 12 months or more - Gross unrealized losses		0
Available-for-sale, 12 months or more - Estimated fair value		0
Available-for-sale, Total - Gross unrealized losses		1,044
Available-for-sale, Total - Estimated fair value		71,907
Held-to-maturity Securities [Member]
Investment [Line Items]
Held-to-maturity, Less than 12 months - Gross unrealized losses		580
Held-to-maturity, Less than 12 months - Estimated fair value		62,884
Held-to-maturity, 12 months or more - Gross unrealized losses		40,586
Held-to-maturity, 12 months or more - Estimated fair value		71,189
Held-to-maturity, Total - Gross unrealized losses		41,166
Held-to-maturity, Total - Estimated fair value		134,073
Available-for-sale Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	10,281	12,558
Available-for-sale, Less than 12 months - Estimated fair value	1,853,362	1,254,783
Available-for-sale, 12 months or more - Gross unrealized losses	9,959	129,717
Available-for-sale, 12 months or more - Estimated fair value	621,812	699,056
Available-for-sale, Total - Gross unrealized losses	20,240	142,275
Available-for-sale, Total - Estimated fair value	2,475,174	1,953,839
Available-for-sale Securities [Member] | Municipal Securities [Member]
Investment [Line Items]
Available-for-sale, 12 months or more - Gross unrealized losses	2,905
Available-for-sale, 12 months or more - Estimated fair value	12,097
Available-for-sale, Total - Gross unrealized losses	2,905
Available-for-sale, Total - Estimated fair value	$ 12,097
Asset-backed Securities [Member] | Trust Preferred Securities - Banks And Insurance [Member]
Investment [Line Items]
Held-to-maturity, Less than 12 months - Gross unrealized losses		53
Held-to-maturity, Less than 12 months - Estimated fair value		122
Held-to-maturity, 12 months or more - Gross unrealized losses		40,309
Held-to-maturity, 12 months or more - Estimated fair value		57,186
Held-to-maturity, Total - Gross unrealized losses		40,362
Held-to-maturity, Total - Estimated fair value		57,308
Available-for-sale, Less than 12 months - Gross unrealized losses		0
Available-for-sale, Less than 12 months - Estimated fair value		0
Available-for-sale, 12 months or more - Gross unrealized losses		121,984
Available-for-sale, 12 months or more - Estimated fair value		405,605
Available-for-sale, Total - Gross unrealized losses		121,984
Available-for-sale, Total - Estimated fair value		405,605
Asset-backed Securities [Member] | Auction Rate Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses		7
Available-for-sale, Less than 12 months - Estimated fair value		1,607
Available-for-sale, 12 months or more - Gross unrealized losses		0
Available-for-sale, 12 months or more - Estimated fair value		0
Available-for-sale, Total - Gross unrealized losses		7
Available-for-sale, Total - Estimated fair value		$ 1,607