FAIR VALUE DISCLOSURES - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	$ 16,327	$ 12,687
Financial assets
Investment securities held-to-maturity	633,722	654,008
Other investments	53,070	53,140
Deposits
Noninterest-bearing	1,572,636	1,662,058
Savings	2,450,196	2,462,420
Time	1,545,273	1,317,105
Carrying value
Financial assets
Cash and short-term investments	126,781	184,624
Investment securities held-to-maturity	633,722	654,008
Other investments	53,070	53,140
Loans held for sale	8,048	11,502
Loans and leases	6,047,641	5,959,162
Interest Receivable	25,842	24,496
Deposits
Deposits	7,010,504	6,895,046
Short-term borrowings	658,332	814,565
Long-term debt	169,695	119,654
Interest Payable	4,091	5,104
Fair value
Financial assets
Cash and short-term investments	126,781	184,624
Investment securities held-to-maturity	623,967	653,101
Loans held for sale	8,048	11,502
Loans and leases	6,098,950	6,006,656
Interest Receivable	25,842	24,496
Deposits
Deposits	6,994,627	6,884,615
Short-term borrowings	658,332	814,565
Long-term debt	165,569	117,908
Interest Payable	4,091	5,104
Fair Value, Inputs, Level 1 [Member] | Fair value
Financial assets
Cash and short-term investments	126,781	184,624
Investment securities held-to-maturity	0	0
Loans held for sale	0	0
Loans and leases	0	0
Interest Receivable	0	0
Deposits
Deposits	0	0
Short-term borrowings	658,332	814,565
Long-term debt	0	0
Interest Payable	375	204
Fair Value, Inputs, Level 2 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	623,967	653,101
Loans held for sale	8,048	11,502
Loans and leases	0	0
Interest Receivable	8,232	8,265
Deposits
Deposits	6,994,627	6,884,615
Short-term borrowings	0	0
Long-term debt	165,569	117,908
Interest Payable	3,716	4,900
Fair Value, Inputs, Level 3 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	0	0
Loans held for sale	0	0
Loans and leases	6,098,950	6,006,656
Interest Receivable	17,610	16,231
Deposits
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Interest Payable	$ 0	$ 0