FAIR VALUE - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	$ 1,077,573	$ 1,007,540
Transfers between Level 1 and Level 2
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0	0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	0	0
U. S. government agency
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	115	955
State and municipal
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	398,126	369,286
Mortgage-backed securities-residential (Government Sponsored Entity)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	383,254	446,630
Collateralized mortgage obligations (Government Sponsored Entity)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	286,395	179,401
Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	4,670	4,670
Other securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	5,013	6,598
Recurring basis | Carrying Value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	1,077,573	1,007,540
Mortgage banking derivatives	621	648
Interest rate derivative	275
Recurring basis | Carrying Value | Interest Rate Swap
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	3,657	3,003
Derivative liability	3,657	3,003
Recurring basis | Carrying Value | U. S. government agency
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	115	955
Recurring basis | Carrying Value | State and municipal
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	398,126	369,286
Recurring basis | Carrying Value | Mortgage-backed securities-residential (Government Sponsored Entity)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	383,254	446,630
Recurring basis | Carrying Value | Collateralized mortgage obligations (Government Sponsored Entity)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	286,395	179,401
Recurring basis | Carrying Value | Equity securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	4,670	4,670
Recurring basis | Carrying Value | Other securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	5,013	6,598
Recurring basis | Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	4,670	4,670
Recurring basis | Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	1,058,553	986,152
Mortgage banking derivatives	621	648
Interest rate derivative	275
Recurring basis | Estimated Fair Value | Significant Other Observable Inputs (Level 2) | Interest Rate Swap
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	3,657	3,003
Derivative liability	3,657	3,003
Recurring basis | Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	14,350	16,718
Recurring basis | Estimated Fair Value | U. S. government agency | Significant Other Observable Inputs (Level 2)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	115	955
Recurring basis | Estimated Fair Value | State and municipal | Significant Other Observable Inputs (Level 2)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	388,789	359,166
Recurring basis | Estimated Fair Value | State and municipal | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	9,337	10,120
Recurring basis | Estimated Fair Value | Mortgage-backed securities-residential (Government Sponsored Entity) | Significant Other Observable Inputs (Level 2)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	383,254	446,630
Recurring basis | Estimated Fair Value | Collateralized mortgage obligations (Government Sponsored Entity) | Significant Other Observable Inputs (Level 2)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	286,395	179,401
Recurring basis | Estimated Fair Value | Equity securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	4,670	4,670
Recurring basis | Estimated Fair Value | Other securities | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	$ 5,013	$ 6,598