INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Available-for-Sale Portfolio [Abstract]
Amortized cost	$ 2,725,232	$ 2,742,278
Gross unrealized gains	164,940	69,254
Gross unrealized losses	309	3,419
Fair value	2,889,863	2,808,113
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	2,724,981
Fair value	2,889,446
Other Securities [Abstract]
Amortized cost	41,438	39,827
Fair value	41,438	39,827
U.S. Treasury and Agency Obligations [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	1,871,049	1,866,819
Gross unrealized gains	121,608	35,186
Gross unrealized losses	0	2,027
Fair value	1,992,657	1,899,978
Obligations of State and Political Subdivisions [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	611,129	640,455
Gross unrealized gains	34,360	26,487
Gross unrealized losses	1	59
Fair value	645,488	666,883
Government Agency Mortgage-Backed Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	215,191	205,220
Gross unrealized gains	8,235	6,906
Gross unrealized losses	287	1,261
Fair value	223,139	210,865
Corporate Debt Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	16,606	16,672
Gross unrealized gains	54	66
Gross unrealized losses	0	58
Fair value	16,660	16,680
Government Agency Collateralized Mortgage Obligations [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	11,006	12,862
Gross unrealized gains	496	446
Gross unrealized losses	0	0
Fair value	11,502	13,308
Marketable Equity Securities [Member]
Available For Sale Equity Securities Amortized Cost Basis [Abstract]
Amortized cost	251	250
Gross unrealized gains	187	163
Gross unrealized losses	21	14
Fair value	417	399
Federal Home Loan Bank Common Stock [Member]
Other Securities [Abstract]
Amortized cost	17,732	19,317
Fair value	17,732	19,317
Federal Reserve Bank Common Stock [Member]
Other Securities [Abstract]
Amortized cost	19,780	16,050
Fair value	19,780	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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