INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Available-for-Sale Portfolio [Abstract]
Amortized cost	$ 2,702,088	$ 2,742,278
Gross unrealized gains	140,429	69,254
Gross unrealized losses	262	3,419
Fair value	2,842,255	2,808,113
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	2,701,837
Fair value	2,841,845
Other Securities [Abstract]
Amortized cost	35,389	39,827
Fair value	35,389	39,827
U.S. Treasury and Agency Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	1,873,698	1,866,819
Gross unrealized gains	102,914	35,186
Gross unrealized losses	0	2,027
Fair value	1,976,612	1,899,978
Obligations of State and Political Subdivisions [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	595,376	640,455
Gross unrealized gains	28,847	26,487
Gross unrealized losses	1	59
Fair value	624,222	666,883
Government Agency Mortgage-Backed Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	216,942	205,220
Gross unrealized gains	8,033	6,906
Gross unrealized losses	242	1,261
Fair value	224,733	210,865
Corporate Debt Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	5,735	16,672
Gross unrealized gains	39	66
Gross unrealized losses	0	58
Fair value	5,774	16,680
Government Agency Collateralized Mortgage Obligations [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	10,086	12,862
Gross unrealized gains	418	446
Gross unrealized losses	0	0
Fair value	10,504	13,308
Marketable Equity Securities [Member]
Available For Sale Equity Securities Amortized Cost Basis [Abstract]
Amortized cost	251	250
Gross unrealized gains	178	163
Gross unrealized losses	19	14
Fair value	410	399
Federal Home Loan Bank Common Stock [Member]
Other Securities [Abstract]
Amortized cost	11,682	19,317
Fair value	11,682	19,317
Federal Reserve Bank Common Stock [Member]
Other Securities [Abstract]
Amortized cost	19,781	16,050
Fair value	19,781	16,050
Other Equity Securities [Member]
Other Securities [Abstract]
Amortized cost	3,926	4,460
Fair value	$ 3,926	$ 4,460

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