Investment Securities (Amortized Cost Table) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Securities available for sale
Available-for-sale Securities, Amortized Cost	$ 3,183,259	$ 2,848,771	$ 3,406,355
Available-for-sale Securities, Gross Unrealized Gains	75,719	85,122	102,037
Available-for-sale Securities, Gross Unrealized Losses	(15,143)	(12,922)	(16,745)
Available-for-sale Securities, Fair Value	3,243,835	2,920,971	3,491,647
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	665,589	622,121	100,840
Held-to-maturity Securities, Unrecognized Holding Gain	8,495	8,764	3,025
Held-to-maturity Securities, Unrecognized Holding Loss	(583)	(86)	0
Held-to-maturity Securities, Fair Value	665,589	622,121	100,840
Held-to-maturity Securities, Fair Value	673,501	630,799	103,865
US Government Agencies Debt Securities [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost			35,340
Available-for-sale Securities, Gross Unrealized Gains			115
Available-for-sale Securities, Gross Unrealized Losses			0
Available-for-sale Securities, Fair Value			35,455
U.S. States and political subdivisions [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	249,750	253,198	365,543
Available-for-sale Securities, Gross Unrealized Gains	13,646	15,235	21,733
Available-for-sale Securities, Gross Unrealized Losses	(790)	(229)	(751)
Available-for-sale Securities, Fair Value	262,606	268,204	386,525
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	292,689	270,005	100,840
Held-to-maturity Securities, Unrecognized Holding Gain	5,041	5,126	3,025
Held-to-maturity Securities, Unrecognized Holding Loss	(244)	(70)	0
Held-to-maturity Securities, Fair Value	297,486	275,061	103,865
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	1,109,905	1,058,005	1,401,241
Available-for-sale Securities, Gross Unrealized Gains	43,084	49,058	53,388
Available-for-sale Securities, Gross Unrealized Losses	(663)	0	(213)
Available-for-sale Securities, Fair Value	1,152,326	1,107,063	1,454,416
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	58,827	52,014	27,689
Available-for-sale Securities, Gross Unrealized Gains	406	428	34
Available-for-sale Securities, Gross Unrealized Losses	(659)	(406)	(60)
Available-for-sale Securities, Fair Value	58,574	52,036	27,663
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	40,413	33,165
Held-to-maturity Securities, Unrecognized Holding Gain	774	812
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	41,187	33,977
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	1,591,341	1,311,501	1,226,260
Available-for-sale Securities, Gross Unrealized Gains	16,292	18,180	25,046
Available-for-sale Securities, Gross Unrealized Losses	(2,354)	(260)	(2)
Available-for-sale Securities, Fair Value	1,605,279	1,329,421	1,251,304
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	137,839	123,563
Held-to-maturity Securities, Unrecognized Holding Gain	680	533
Held-to-maturity Securities, Unrecognized Holding Loss	0	(16)
Held-to-maturity Securities, Fair Value	138,519	124,080
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	11	11	41,741
Available-for-sale Securities, Gross Unrealized Gains	0	0	91
Available-for-sale Securities, Gross Unrealized Losses	0	0	0
Available-for-sale Securities, Fair Value	11	11	41,832
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	108,658	109,260	147,214
Available-for-sale Securities, Gross Unrealized Gains	2,291	2,221	675
Available-for-sale Securities, Gross Unrealized Losses	(347)	(138)	(534)
Available-for-sale Securities, Fair Value	110,602	111,343	147,355
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	98,887	98,924
Held-to-maturity Securities, Unrecognized Holding Gain	385	772
Held-to-maturity Securities, Unrecognized Holding Loss	(339)	0
Held-to-maturity Securities, Fair Value	98,933	99,696
Corporate debt securities [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	61,555	61,541	158,019
Available-for-sale Securities, Gross Unrealized Gains	0	0	955
Available-for-sale Securities, Gross Unrealized Losses	(10,330)	(11,889)	(15,185)
Available-for-sale Securities, Fair Value	51,225	49,652	143,789
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	95,761	96,464
Held-to-maturity Securities, Unrecognized Holding Gain	1,615	1,521
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	97,376	97,985
Debt Securities [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	3,180,047	2,845,530	3,403,047
Available-for-sale Securities, Gross Unrealized Gains	75,719	85,122	102,037
Available-for-sale Securities, Gross Unrealized Losses	(15,143)	(12,922)	(16,745)
Available-for-sale Securities, Fair Value	3,240,623	2,917,730	3,488,339
Marketable equity securities [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	3,212	3,241	3,308
Available-for-sale Securities, Gross Unrealized Gains	0	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0	0
Available-for-sale Securities, Fair Value	$ 3,212	$ 3,241	$ 3,308

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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