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, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	$ 1,280,761	$ 1,022,182
U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	36,957	9,383
Obligations of U. S. Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	150,504	100,170
Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	531,134	480,374
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	530,749	401,232
Corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	31,417	31,023
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	36,957	9,383
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	36,957	9,383
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]
Debt 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]
Debt 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]
Debt 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]
Debt 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]
Debt securities available-for-sale, at fair value	1,223,482	992,438
Significant Other Observable Inputs (Level 2) | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt 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]
Debt securities available-for-sale, at fair value	150,504	100,170
Significant Other Observable Inputs (Level 2) | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	511,030	460,248
Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	530,749	401,232
Significant Other Observable Inputs (Level 2) | Corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	31,199	30,788
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt securities available-for-sale, at fair value	20,322	20,361
Significant Unobservable Inputs (Level 3) | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt 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]
Debt 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]
Debt securities available-for-sale, at fair value	20,104	20,126
Significant Unobservable Inputs (Level 3) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Debt 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]
Debt securities available-for-sale, at fair value	$ 218	$ 235