Investment Securities (Amortized Cost Table and Fair Value of Held to Maturity and Available for Sale Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Securities available for sale
Available-for-sale Securities, Amortized Cost	$ 4,274,004	$ 4,005,782	$ 3,851,202
Available-for-sale Debt Securities, Gross Unrealized Gains	65,212	18,980	30,747
Available-for-sale Debt Securities, Gross Unrealized Losses	(20,528)	(57,027)	(43,440)
Available-for-sale	4,318,688	3,967,735	3,838,509
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	2,514,161	2,674,093	2,787,513
Held-to-maturity Securities, Gross Unrealized Gains	38,966	28,375	17,579
Held-to-maturity Securities, Gross Unrealized Losses	(7,387)	(43,349)	(44,972)
Held-to-maturity Securities, Fair Value	2,545,740	2,659,119	2,760,120
US Treasury Securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	4,996	5,001	5,004
Available-for-sale Debt Securities, Gross Unrealized Gains	1	0	1
Available-for-sale Debt Securities, Gross Unrealized Losses	0	(1)	0
Available-for-sale	4,997	5,000	5,005
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	0
Held-to-maturity Securities, Fair Value	0
US Government Agencies Debt Securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	2,500	2,500	2,500
Available-for-sale Debt Securities, Gross Unrealized Gains	28	0	10
Available-for-sale Debt Securities, Gross Unrealized Losses	0	(2)	0
Available-for-sale	2,528	2,498	2,510
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	25,000	25,000	25,000
Held-to-maturity Securities, Gross Unrealized Gains	35	19	0
Held-to-maturity Securities, Gross Unrealized Losses	0	0	(323)
Held-to-maturity Securities, Fair Value	25,035	25,019	24,677
U.S. States and political subdivisions debt securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	147,807	188,829	203,449
Available-for-sale Debt Securities, Gross Unrealized Gains	3,742	4,170	5,191
Available-for-sale Debt Securities, Gross Unrealized Losses	(2)	(204)	(1,023)
Available-for-sale	151,547	192,795	207,617
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	540,425	571,738	529,441
Held-to-maturity Securities, Gross Unrealized Gains	15,713	22,180	8,104
Held-to-maturity Securities, Gross Unrealized Losses	(265)	(262)	(1,942)
Held-to-maturity Securities, Fair Value	555,873	593,656	535,603
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Amortized Cost	840,250	900,358	947,347
Available-for-sale Debt Securities, Gross Unrealized Gains	20,064	11,325	18,068
Available-for-sale Debt Securities, Gross Unrealized Losses	(67)	(5,454)	(4,563)
Available-for-sale	860,247	906,229	960,852
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	467,462	507,908	555,273
Held-to-maturity Securities, Gross Unrealized Gains	12,367	4,767	6,919
Held-to-maturity Securities, Gross Unrealized Losses	0	(2,999)	(2,940)
Held-to-maturity Securities, Fair Value	479,829	509,676	559,252
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Amortized Cost	198,069	173,912	171,842
Available-for-sale Debt Securities, Gross Unrealized Gains	4,095	220	643
Available-for-sale Debt Securities, Gross Unrealized Losses	(116)	(2,023)	(2,147)
Available-for-sale	202,048	172,109	170,338
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	87,964	64,951	57,462
Held-to-maturity Securities, Gross Unrealized Gains	1,991	294	412
Held-to-maturity Securities, Gross Unrealized Losses	(42)	(574)	(219)
Held-to-maturity Securities, Fair Value	89,913	64,671	57,655
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises
Securities available for sale
Available-for-sale Securities, Amortized Cost	2,325,707	2,155,808	1,968,918
Available-for-sale Debt Securities, Gross Unrealized Gains	30,400	2,659	4,779
Available-for-sale Debt Securities, Gross Unrealized Losses	(3,089)	(30,147)	(24,308)
Available-for-sale	2,353,018	2,128,320	1,949,389
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	1,060,496	1,161,340	1,267,321
Held-to-maturity Securities, Gross Unrealized Gains	4,327	75	445
Held-to-maturity Securities, Gross Unrealized Losses	(6,670)	(35,881)	(35,025)
Held-to-maturity Securities, Fair Value	1,058,153	1,125,534	1,232,741
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency
Securities available for sale
Available-for-sale Securities, Amortized Cost	3	4	5
Available-for-sale Debt Securities, Gross Unrealized Gains	0	0	0
Available-for-sale Debt Securities, Gross Unrealized Losses	0	0	0
Available-for-sale	3	4	5
Securities held to maturity
Held-to-maturity Securities, 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
Available-for-sale Securities, Amortized Cost	392,205	217,008	227,889
Available-for-sale Debt Securities, Gross Unrealized Gains	6,528	580	1,254
Available-for-sale Debt Securities, Gross Unrealized Losses	(122)	(1,269)	(705)
Available-for-sale	398,611	216,319	228,438
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	246,509	255,359	263,741
Held-to-maturity Securities, Gross Unrealized Gains	3,559	676	1,004
Held-to-maturity Securities, Gross Unrealized Losses	(410)	(3,611)	(4,523)
Held-to-maturity Securities, Fair Value	249,658	252,424	260,222
Collateralized Loan Obligations
Securities available for sale
Available-for-sale Securities, Amortized Cost	297,939	297,831	259,743
Available-for-sale Debt Securities, Gross Unrealized Gains	354	26	801
Available-for-sale Debt Securities, Gross Unrealized Losses	(6,499)	(8,446)	(2,463)
Available-for-sale	291,794	289,411	258,081
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	0
Held-to-maturity Securities, Fair Value	0
Corporate debt securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	61,740	61,710	61,681
Available-for-sale Debt Securities, Gross Unrealized Gains	0	0	0
Available-for-sale Debt Securities, Gross Unrealized Losses	(10,633)	(9,481)	(8,231)
Available-for-sale	51,107	52,229	53,450
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	86,305	87,797	89,275
Held-to-maturity Securities, Gross Unrealized Gains	974	364	695
Held-to-maturity Securities, Gross Unrealized Losses	0	(22)	0
Held-to-maturity Securities, Fair Value	87,279	88,139	89,970
Debt Securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	4,271,216	4,002,961	3,848,378
Available-for-sale Debt Securities, Gross Unrealized Gains	65,212	18,980	30,747
Available-for-sale Debt Securities, Gross Unrealized Losses	(20,528)	(57,027)	(43,440)
Available-for-sale	4,315,900	3,964,914	3,835,685
Marketable Equity Securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	2,788	2,821	2,824
Available-for-sale Debt Securities, Gross Unrealized Gains	0	0	0
Available-for-sale Debt Securities, Gross Unrealized Losses	0	0	0
Available-for-sale	2,788	2,821	2,824
Other Security Investments
Securities available for sale
Available-for-sale Securities, Amortized Cost			0
Available-for-sale Debt Securities, Gross Unrealized Gains			0
Available-for-sale Debt Securities, Gross Unrealized Losses			0
Available-for-sale			0
Equity Securities
Securities available for sale
Available-for-sale Securities, Amortized Cost	2,788		2,824
Available-for-sale Debt Securities, Gross Unrealized Gains	0		0
Available-for-sale Debt Securities, Gross Unrealized Losses	0		0
Available-for-sale	$ 2,788	$ 2,821	$ 2,824

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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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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-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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