SECURITIES - Summary of Amortized Cost and Fair Value of Available-For-Sale Securities and Held-To-Maturity Securities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale Securities, Amortized Cost	$ 894,340	$ 751,591
Available-for-sale Securities, Gross Unrealized Gains	33,620	14,419
Available-for-sale Securities, Gross Unrealized Losses	755	923
Available-for-sale securities, Fair Value	927,205	765,087
U.S Treasury
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale Securities, Amortized Cost	9,097	4,967
Available-for-sale Securities, Gross Unrealized Gains	346	0
Available-for-sale Securities, Gross Unrealized Losses	0	73
Available-for-sale securities, Fair Value	9,443	4,894
Obligations of U.S. government agencies and sponsored entities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale Securities, Amortized Cost	97,210	76,699
Available-for-sale Securities, Gross Unrealized Gains	3,014	1,475
Available-for-sale Securities, Gross Unrealized Losses	11	224
Available-for-sale securities, Fair Value	100,213	77,950
Tax-exempt and taxable obligations of states and municipal subdivisions
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale Securities, Amortized Cost	377,573	253,527
Available-for-sale Securities, Gross Unrealized Gains	12,874	5,602
Available-for-sale Securities, Gross Unrealized Losses	598	147
Available-for-sale securities, Fair Value	389,849	258,982
Mortgage-backed securities - residential
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale Securities, Amortized Cost	259,611	263,229
Available-for-sale Securities, Gross Unrealized Gains	10,255	4,726
Available-for-sale Securities, Gross Unrealized Losses	71	107
Available-for-sale securities, Fair Value	269,795	267,848
Mortgage-backed securities - commercial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale Securities, Amortized Cost	122,802	125,292
Available-for-sale Securities, Gross Unrealized Gains	6,273	2,398
Available-for-sale Securities, Gross Unrealized Losses	52	223
Available-for-sale securities, Fair Value	129,023	127,467
Corporate obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale Securities, Amortized Cost	28,047	27,877
Available-for-sale Securities, Gross Unrealized Gains	858	218
Available-for-sale Securities, Gross Unrealized Losses	23	149
Available-for-sale securities, Fair Value	$ 28,882	$ 27,946