Investment Securities (Amortized Cost Table) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Securities available for sale
Available-for-sale Securities, Amortized Cost	$ 3,329,117	$ 2,848,771
Available-for-sale Securities, Fair Value	3,273,174	2,920,971
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	2,935,688	622,121
Held-to-maturity Securities, Fair Value	2,935,688	622,121
Held-to-maturity Securities, Fair Value	2,824,240	630,799
Available-for-sale Securities, Gross Unrealized Gain at End of Period	34,277	85,122
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(90,220)	(12,922)
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	6,761	8,764
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	118,209	86
U.S. Government agencies
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	25,000
Held-to-maturity Securities, Fair Value	23,652
Held-to-maturity Securities, Fair Value	23,652
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	0
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	1,348
U.S. States and political subdivisions
Securities available for sale
Available-for-sale Securities, Amortized Cost	258,787	253,198
Available-for-sale Securities, Fair Value	262,367	268,204
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	480,703	270,005
Held-to-maturity Securities, Fair Value	475,579	275,061
Held-to-maturity Securities, Fair Value	475,579
Available-for-sale Securities, Gross Unrealized Gain at End of Period	7,376	15,235
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(3,796)	(229)
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	5,335	5,126
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	10,459	70
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Amortized Cost	962,687	1,058,005
Available-for-sale Securities, Fair Value	969,922	1,107,063
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	569,960
Held-to-maturity Securities, Fair Value	559,451
Held-to-maturity Securities, Fair Value	559,451
Available-for-sale Securities, Gross Unrealized Gain at End of Period	21,662	49,058
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(14,427)	0
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	1,108
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	11,617
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Amortized Cost	72,048	52,014
Available-for-sale Securities, Fair Value	69,567	52,036
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	56,596	33,165
Held-to-maturity Securities, Fair Value	55,406	33,977
Held-to-maturity Securities, Fair Value	55,406
Available-for-sale Securities, Gross Unrealized Gain at End of Period	7	428
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(2,488)	(406)
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	0	812
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	1,190	0
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Amortized Cost	1,566,262	1,311,501
Available-for-sale Securities, Fair Value	1,518,393	1,329,421
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	1,464,732	123,563
Held-to-maturity Securities, Fair Value	1,382,914	124,080
Held-to-maturity Securities, Fair Value	1,382,914
Available-for-sale Securities, Gross Unrealized Gain at End of Period	4,199	18,180
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(52,068)	(260)
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	0	533
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	81,818	16
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency
Securities available for sale
Available-for-sale Securities, Amortized Cost	9	11
Available-for-sale Securities, Fair Value	9	11
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	0
Held-to-maturity Securities, Fair Value	0
Available-for-sale Securities, Gross Unrealized Gain at End of Period	0	0
Available-for-sale Securities, Gross Unrealized Loss at End of Period	0	0
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Amortized Cost	104,152	109,260
Available-for-sale Securities, Fair Value	102,268	111,343
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	240,069	98,924
Held-to-maturity Securities, Fair Value	229,023	99,696
Held-to-maturity Securities, Fair Value	229,023
Available-for-sale Securities, Gross Unrealized Gain at End of Period	273	2,221
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(2,157)	(138)
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	6	772
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	11,052	0
Collateralized Loan Obligations
Securities available for sale
Available-for-sale Securities, Amortized Cost	297,259
Available-for-sale Securities, Fair Value	293,687
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	0
Held-to-maturity Securities, Fair Value	0
Available-for-sale Securities, Gross Unrealized Gain at End of Period	760
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(4,332)
Corporate bonds
Securities available for sale
Available-for-sale Securities, Amortized Cost	61,596	61,541
Available-for-sale Securities, Fair Value	50,644	49,652
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	93,628	96,464
Held-to-maturity Securities, Fair Value	93,211	97,985
Held-to-maturity Securities, Fair Value	93,211
Available-for-sale Securities, Gross Unrealized Gain at End of Period	0	0
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(10,952)	(11,889)
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	308	1,521
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	725	0
Total debt securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	3,322,800	2,845,530
Available-for-sale Securities, Fair Value	3,266,857	2,917,730
Securities held to maturity
Available-for-sale Securities, Gross Unrealized Gain at End of Period	34,277	85,122
Available-for-sale Securities, Gross Unrealized Loss at End of Period	(90,220)	(12,922)
Marketable equity securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	3,036	3,241
Available-for-sale Securities, Fair Value	3,036	3,241
Securities held to maturity
Available-for-sale Securities, Gross Unrealized Gain at End of Period	0	0
Available-for-sale Securities, Gross Unrealized Loss at End of Period	0	0
Non-marketable equity securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	3,281
Available-for-sale Securities, Fair Value	3,281
Securities held to maturity
Available-for-sale Securities, Gross Unrealized Gain at End of Period	0
Available-for-sale Securities, Gross Unrealized Loss at End of Period	0
Total equity securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	6,317
Available-for-sale Securities, Fair Value	6,317
Securities held to maturity
Available-for-sale Securities, Gross Unrealized Gain at End of Period	0
Available-for-sale Securities, Gross Unrealized Loss at End of Period	0
U.S. Treasury obligations
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	5,000
Held-to-maturity Securities, Fair Value	5,004
Held-to-maturity Securities, Fair Value	5,004
Held-to-maturity Securities, Unrecognized Holding Gain End of Period	4
Held-to-Maturity Securities, Unrecognized Holding Loss End of Period	$ 0