INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-Sale Portfolio [Abstract]
Amortized cost	$ 2,706,863	$ 2,742,278
Gross unrealized gains	47,463	69,254
Gross unrealized losses	5,670	3,419
Fair value	2,748,656	2,808,113
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	2,706,611
Estimated fair value	2,748,204
Other Securities [Abstract]
Amortized cost	35,736	39,827
Estimated fair value	35,736	39,827
U.S. Treasury and Agency Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	1,876,358	1,866,819
Gross unrealized gains	28,522	35,186
Gross unrealized losses	2,118	2,027
Estimated fair value	1,902,762	1,899,978
Obligations of State and Political Subdivisions [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	582,655	640,455
Gross unrealized gains	13,389	26,487
Gross unrealized losses	1,054	59
Estimated fair value	594,990	666,883
Government Agency Mortgage-Backed Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	232,657	205,220
Gross unrealized gains	5,040	6,906
Gross unrealized losses	2,467	1,261
Estimated fair value	235,230	210,865
Corporate Debt Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	5,716	16,672
Gross unrealized gains	2	66
Gross unrealized losses	31	58
Estimated fair value	5,687	16,680
Government Agency Collateralized Mortgage Obligations [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	9,225	12,862
Gross unrealized gains	310	446
Gross unrealized losses	0	0
Estimated fair value	9,535	13,308
Marketable Equity Security [Member]
Available For Sale Equity Securities Amortized Cost Basis [Abstract]
Amortized cost	252	250
Gross unrealized gains	200	163
Gross unrealized losses	0	14
Estimated fair value	452	399
Federal Home Loan Bank Common Stock [Member]
Other Securities [Abstract]
Amortized cost	12,191	19,317
Estimated fair value	12,191	19,317
Federal Reserve Bank Common Stock [Member]
Other Securities [Abstract]
Amortized cost	19,781	16,050
Estimated fair value	19,781	16,050
Other Equity Securities [Member]
Other Securities [Abstract]
Amortized cost	3,764	4,460
Estimated fair value	$ 3,764	$ 4,460

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