Investment Securities (Amortized Cost) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Securities available for sale
Amortized cost	$ 4,005,782	$ 3,562,537
Available-for-sale Securities, Gross Unrealized Gains	18,980	35,382
Available-for-sale Securities, Gross Unrealized Losses	(57,027)	(52,631)
Available-for-sale	3,967,735	3,545,288
Securities held to maturity
Amortized cost	2,674,093	2,903,609
Held-to-maturity Securities, Gross Unrealized Gains	28,375	22,108
Held-to-maturity Securities, Gross Unrealized Losses	(43,349)	(49,797)
Held-to-maturity Securities, Fair Value	2,659,119	2,875,920
U.S. Treasury obligations
Securities available for sale
Amortized cost	5,001
Available-for-sale Securities, Gross Unrealized Gains	0
Available-for-sale Securities, Gross Unrealized Losses	(1)
Available-for-sale	5,000
Securities held to maturity
Amortized cost	0	5,000
Held-to-maturity Securities, Gross Unrealized Gains		0
Held-to-maturity Securities, Gross Unrealized Losses		0
Held-to-maturity Securities, Fair Value	0	5,000
U.S. Government agencies
Securities available for sale
Amortized cost	2,500	2,500
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	(2)	(18)
Available-for-sale	2,498	2,482
Securities held to maturity
Amortized cost	25,000	25,000
Held-to-maturity Securities, Gross Unrealized Gains	19	0
Held-to-maturity Securities, Gross Unrealized Losses	0	(537)
Held-to-maturity Securities, Fair Value	25,019	24,463
U.S. States and political subdivisions
Securities available for sale
Amortized cost	188,829	221,052
Available-for-sale Securities, Gross Unrealized Gains	4,170	6,756
Available-for-sale Securities, Gross Unrealized Losses	(204)	(466)
Available-for-sale	192,795	227,342
Securities held to maturity
Amortized cost	571,738	517,824
Held-to-maturity Securities, Gross Unrealized Gains	22,180	12,645
Held-to-maturity Securities, Gross Unrealized Losses	(262)	(191)
Held-to-maturity Securities, Fair Value	593,656	530,278
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Amortized cost	900,358	951,839
Available-for-sale Securities, Gross Unrealized Gains	11,325	22,377
Available-for-sale Securities, Gross Unrealized Losses	(5,454)	(3,218)
Available-for-sale	906,229	970,998
Securities held to maturity
Amortized cost	507,908	580,727
Held-to-maturity Securities, Gross Unrealized Gains	4,767	7,495
Held-to-maturity Securities, Gross Unrealized Losses	(2,999)	(3,045)
Held-to-maturity Securities, Fair Value	509,676	585,177
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Amortized cost	173,912	104,176
Available-for-sale Securities, Gross Unrealized Gains	220	598
Available-for-sale Securities, Gross Unrealized Losses	(2,023)	(1,371)
Available-for-sale	172,109	103,403
Securities held to maturity
Amortized cost	64,951	58,143
Held-to-maturity Securities, Gross Unrealized Gains	294	281
Held-to-maturity Securities, Gross Unrealized Losses	(574)	(329)
Held-to-maturity Securities, Fair Value	64,671	58,095
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Amortized cost	2,155,808	1,698,015
Available-for-sale Securities, Gross Unrealized Gains	2,659	4,777
Available-for-sale Securities, Gross Unrealized Losses	(30,147)	(26,225)
Available-for-sale	2,128,320	1,676,567
Securities held to maturity
Amortized cost	1,161,340	1,368,534
Held-to-maturity Securities, Gross Unrealized Gains	75	718
Held-to-maturity Securities, Gross Unrealized Losses	(35,881)	(38,875)
Held-to-maturity Securities, Fair Value	1,125,534	1,330,377
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency
Securities available for sale
Amortized cost	4	7
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale	4	7
Securities held to maturity
Amortized cost	0
Held-to-maturity Securities, Fair Value	0
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Amortized cost	217,008	222,876
Available-for-sale Securities, Gross Unrealized Gains	580	863
Available-for-sale Securities, Gross Unrealized Losses	(1,269)	(1,405)
Available-for-sale	216,319	222,334
Securities held to maturity
Amortized cost	255,359	257,642
Held-to-maturity Securities, Gross Unrealized Gains	676	557
Held-to-maturity Securities, Gross Unrealized Losses	(3,611)	(6,768)
Held-to-maturity Securities, Fair Value	252,424	251,431
Collateralized Loan Obligations
Securities available for sale
Amortized cost	297,831	297,446
Available-for-sale Securities, Gross Unrealized Gains	26	11
Available-for-sale Securities, Gross Unrealized Losses	(8,446)	(9,613)
Available-for-sale	289,411	287,844
Securities held to maturity
Amortized cost	0
Held-to-maturity Securities, Fair Value	0
Corporate bonds
Securities available for sale
Amortized cost	61,710	61,652
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	(9,481)	(10,315)
Available-for-sale	52,229	51,337
Securities held to maturity
Amortized cost	87,797	90,739
Held-to-maturity Securities, Gross Unrealized Gains	364	412
Held-to-maturity Securities, Gross Unrealized Losses	(22)	(52)
Held-to-maturity Securities, Fair Value	88,139	91,099
Total debt securities
Securities available for sale
Amortized cost	4,002,961	3,559,563
Available-for-sale Securities, Gross Unrealized Gains	18,980	35,382
Available-for-sale Securities, Gross Unrealized Losses	(57,027)	(52,631)
Available-for-sale	3,964,914	3,542,314
Marketable equity securities
Securities available for sale
Amortized cost	2,821	2,974
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale	2,821	2,974
Total equity securities
Securities available for sale
Amortized cost	2,821
Available-for-sale Securities, Gross Unrealized Gains	0
Available-for-sale Securities, Gross Unrealized Losses	0
Available-for-sale	$ 2,821	$ 2,974

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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

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