FAIR VALUE DISCLOSURES AND REPORTING, THE FAIR VALUE OPTION AND FAIR VALUE MEASUREMENTS - Fair Value of Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	$ 762,977	$ 765,087
U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	5,308	4,894
Obligations of U. S. Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	72,880	77,950
Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	274,163	258,982
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	382,900	395,315
Corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	27,726	27,946
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	5,308	4,894
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	5,308	4,894
Quoted Prices in Active Markets for Identical Assets (Level 1) | Obligations of U. S. Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	737,976	749,440
Significant Other Observable Inputs (Level 2) | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	0	0
Significant Other Observable Inputs (Level 2) | Obligations of U. S. Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	72,880	77,950
Significant Other Observable Inputs (Level 2) | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	254,981	248,637
Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	382,900	395,315
Significant Other Observable Inputs (Level 2) | Corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	27,215	27,538
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	19,693	10,753
Significant Unobservable Inputs (Level 3) | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	0	0
Significant Unobservable Inputs (Level 3) | Obligations of U. S. Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	0	0
Significant Unobservable Inputs (Level 3) | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	19,182	10,345
Significant Unobservable Inputs (Level 3) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	0	0
Significant Unobservable Inputs (Level 3) | Corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	$ 511	$ 408