Investment Securities (Amortization Cost, Gross Unrealized Gains/Losses, and Fair Value) (Details 1) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 2,302,408	$ 2,183,943
Available-for-Sale: Gross Unrealized Gains	26,723	19,539
Available-for-Sale: Gross Unrealized Losses	(12,403)	(17,441)
Available-for-Sale	2,316,728	2,186,041
Held-to-maturity Securities [Abstract]
Held-to-Maturity: Amortized Cost	3,782,702	3,832,997
Held-to-Maturity: Gross Unrealized Gains	34,713	34,274
Held-to-Maturity: Gross Unrealized Losses	(31,774)	(39,744)
Held-to-Maturity: Fair Value	3,785,641	3,827,527
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	430,208	407,478
Available-for-Sale: Gross Unrealized Gains	3,732	2,531
Available-for-Sale: Gross Unrealized Losses	(963)	(1,294)
Available-for-Sale	432,977	408,715
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	650,075	662,231
Available-for-Sale: Gross Unrealized Gains	17,905	11,455
Available-for-Sale: Gross Unrealized Losses	(99)	(1,887)
Available-for-Sale	667,881	671,799
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	268,022	273,044
Available-for-Sale: Gross Unrealized Gains	138	5
Available-for-Sale: Gross Unrealized Losses	(2,911)	(3,870)
Available-for-Sale	265,249	269,179
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	262,834	240,412
Available-for-Sale: Gross Unrealized Gains	3,858	4,577
Available-for-Sale: Gross Unrealized Losses	(1,150)	(1,145)
Available-for-Sale	265,542	243,844
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	613,512	511,234
Available-for-Sale: Gross Unrealized Gains	1,090	971
Available-for-Sale: Gross Unrealized Losses	(4,701)	(5,218)
Available-for-Sale	609,901	506,987
Commercial - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	77,757	89,544
Available-for-Sale: Gross Unrealized Gains	0	0
Available-for-Sale: Gross Unrealized Losses	(2,579)	(4,027)
Available-for-Sale	75,178	85,517
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	954,103	841,190
Available-for-Sale: Gross Unrealized Gains	4,948	5,548
Available-for-Sale: Gross Unrealized Losses	(8,430)	(10,390)
Available-for-Sale	950,621	836,348
Debt Securities Issued by the U.S. Treasury and Government Agencies
Held-to-maturity Securities [Abstract]
Held-to-Maturity: Amortized Cost	500,111	530,149
Held-to-Maturity: Gross Unrealized Gains	613	1,562
Held-to-Maturity: Gross Unrealized Losses	(886)	(771)
Held-to-Maturity: Fair Value	499,838	530,940
Debt Securities Issued by States and Political Subdivisions
Held-to-maturity Securities [Abstract]
Held-to-Maturity: Amortized Cost	240,413	242,295
Held-to-Maturity: Gross Unrealized Gains	14,472	9,991
Held-to-Maturity: Gross Unrealized Losses	0	0
Held-to-Maturity: Fair Value	254,885	252,286
Debt Securities Issued by Corporations
Held-to-maturity Securities [Abstract]
Held-to-Maturity: Amortized Cost	127,666	135,620
Held-to-Maturity: Gross Unrealized Gains	405	416
Held-to-Maturity: Gross Unrealized Losses	(1,326)	(1,528)
Held-to-Maturity: Fair Value	126,745	134,508
Residential - Government Agencies
Held-to-maturity Securities [Abstract]
Held-to-Maturity: Amortized Cost	1,928,530	1,940,076
Held-to-Maturity: Gross Unrealized Gains	15,726	20,567
Held-to-Maturity: Gross Unrealized Losses	(19,602)	(23,861)
Held-to-Maturity: Fair Value	1,924,654	1,936,782
Residential - U.S. Government-Sponsored Enterprises
Held-to-maturity Securities [Abstract]
Held-to-Maturity: Amortized Cost	772,212	752,768
Held-to-Maturity: Gross Unrealized Gains	1,284	798
Held-to-Maturity: Gross Unrealized Losses	(7,144)	(10,919)
Held-to-Maturity: Fair Value	766,352	742,647
Commercial - Government Agencies
Held-to-maturity Securities [Abstract]
Held-to-Maturity: Amortized Cost	213,770	232,089
Held-to-Maturity: Gross Unrealized Gains	2,213	940
Held-to-Maturity: Gross Unrealized Losses	(2,816)	(2,665)
Held-to-Maturity: Fair Value	213,167	230,364
Mortgage-Backed Securities
Held-to-maturity Securities [Abstract]
Held-to-Maturity: Amortized Cost	2,914,512	2,924,933
Held-to-Maturity: Gross Unrealized Gains	19,223	22,305
Held-to-Maturity: Gross Unrealized Losses	(29,562)	(37,445)
Held-to-Maturity: Fair Value	$ 2,904,173	$ 2,909,793

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

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

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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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Amount of accumulated unrealized loss 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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