TIME DEPOSITS AND SHORT-TERM DEBT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Certificates of deposits and other time deposits over $100,000 outstanding	$ 969,600	$ 910,200
Interest expense relating to certificate and other time deposits of $100,000 or more	8,700	8,700	$ 11,400
Maturities of time deposits [Abstract]
2018	274,928
2019	181,176
2020	181,906
2021	230,580
2022	111
Total	868,701
End of Period Balance	546,002	467,937	391,666
Daily Average Balance	456,008	471,360	444,230
Maximum Outstanding at any Month End	654,614	807,607	582,663
Lines of credit with other banks	795,000
Federal Funds Purchased [Member]
Maturities of time deposits [Abstract]
Daily Average Balance	$ 1,678	$ 10,066	$ 4,247
Daily Average Interest Rate (in hundredths)	0.51%	0.17%	0.18%
Maximum Outstanding at any Month End		$ 25,000	$ 10,000
Period from date of sale that securities generally mature	30 days
Securities Sold Under Agreements to Repurchase [Member]
Maturities of time deposits [Abstract]
End of Period Balance	$ 454,002	$ 405,937	$ 388,166
End of Period Interest Rate (in hundredths)	0.26%	0.12%	0.08%
Daily Average Balance	$ 449,672	$ 416,172	$ 436,875
Daily Average Interest Rate (in hundredths)	0.15%	0.09%	0.07%
Maximum Outstanding at any Month End	$ 562,614	$ 558,107	$ 569,163
Federal Reserve Bank Advances [Member]
Maturities of time deposits [Abstract]
Period from date of purchase that borrowings generally mature	90 days
Federal Home Loan Bank [Member]
Maturities of time deposits [Abstract]
End of Period Balance	$ 92,000	$ 62,000	$ 3,500
End of Period Interest Rate (in hundredths)	0.55%	0.31%	4.83%
Daily Average Balance	$ 4,658	$ 45,122	$ 3,108
Daily Average Interest Rate (in hundredths)	0.44%	0.37%	2.60%
Maximum Outstanding at any Month End	$ 92,000	$ 224,500	$ 3,500
Period from date of purchase that borrowings generally mature	30 days