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	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	$ 927,205	$ 765,087
U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	9,443	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	100,213	77,950
Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	389,849	258,982
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	398,818	395,315
Corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available-for-sale, at fair value	28,882	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	9,443	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	9,443	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	906,638	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	100,213	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	378,965	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	398,818	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	28,642	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	11,124	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	10,884	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	$ 240	$ 408