INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Available-for-Sale Portfolio [Abstract]
Amortized cost	$ 2,695,204	$ 2,706,863
Gross unrealized gains	49,983	47,463
Gross unrealized losses	4,297	5,670
Fair value	2,740,890	2,748,656
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	2,694,953
Fair value	2,740,436
Other Securities [Abstract]
Amortized cost	47,828	35,736
Fair value	47,828	35,736
U.S. Treasury and Agency Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	1,878,982	1,876,358
Gross unrealized gains	30,358	28,522
Gross unrealized losses	1,106	2,118
Fair value	1,908,234	1,902,762
Obligations of State and Political Subdivisions [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	564,501	582,655
Gross unrealized gains	14,603	13,389
Gross unrealized losses	446	1,054
Fair value	578,658	594,990
Government Agency Mortgage-Backed Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	237,257	232,657
Gross unrealized gains	4,526	5,040
Gross unrealized losses	2,729	2,467
Fair value	239,054	235,230
Corporate Debt Securities [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	5,697	5,716
Gross unrealized gains	0	2
Gross unrealized losses	16	31
Fair value	5,681	5,687
Government Agency Collateralized Mortgage Obligations [Member]
Available For Sale Debt Securities Amortized Cost Basis [Abstract]
Amortized cost	8,516	9,225
Gross unrealized gains	293	310
Gross unrealized losses	0	0
Fair value	8,809	9,535
Marketable Equity Securities [Member]
Available For Sale Equity Securities Amortized Cost Basis [Abstract]
Amortized cost	251	252
Gross unrealized gains	203	200
Gross unrealized losses	0	0
Fair value	454	452
Federal Home Loan Bank Common Stock [Member]
Other Securities [Abstract]
Amortized cost	5,590	12,191
Fair value	5,590	12,191
Federal Reserve Bank Common Stock [Member]
Other Securities [Abstract]
Amortized cost	19,781	19,781
Fair value	19,781	19,781
Certificates of Deposit [Member]
Other Securities [Abstract]
Amortized cost	18,758	0
Fair value	18,758	0
Other Equity Securities [Member]
Other Securities [Abstract]
Amortized cost	3,699	3,764
Fair value	$ 3,699	$ 3,764

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