FAIR VALUE - Summary of Estimated Fair Values and Carrying Amounts of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Financial assets:
Cash and due from banks	$ 94,892	$ 77,693
Interest-bearing deposits with banks	615,575	39,501
Securities available for sale	466,081	638,291
Securities held to maturity	104,911	135,027
Loans held for sale		12,600
Accrued interest receivable	15,823	10,908
Carrying Amount
Financial assets:
Cash and due from banks	94,892	77,693
Interest-bearing deposits with banks	615,575	39,501
Securities available for sale	466,081	638,291
Securities restricted	23,362	32,879
Securities held to maturity	100,934	133,638
Loans held for sale	10,000	12,643	$ 12,600
Loans, net	4,595,999	3,647,499
Derivatives	59,385	15,437
Accrued interest receivable	15,823	10,908
Financial liabilities:
Certificates of deposit	290,402	307,977
Demand and other deposits	5,078,667	3,506,670
FHLB advances	215,000	435,000
Repurchase agreements	1,353	999
Subordinated debentures	79,024	78,920
Derivatives	67,341	16,645
Accrued interest payable	328	1,467
Fair Value
Financial assets:
Cash and due from banks	94,892	77,693
Interest-bearing deposits with banks	615,575	39,501
Securities available for sale	466,081	638,291
Securities held to maturity	104,911	135,027
Loans held for sale	10,000	12,643
Loans, net	4,645,937	3,685,770
Derivatives	59,385	15,437
Accrued interest receivable	15,823	10,908
Financial liabilities:
Certificates of deposit	293,552	308,660
Demand and other deposits	5,078,667	3,506,670
FHLB advances	222,342	434,622
Repurchase agreements	1,353	999
Subordinated debentures	87,615	81,010
Derivatives	67,341	16,645
Accrued interest payable	328	1,467
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and due from banks	94,892	77,693
Interest-bearing deposits with banks	615,575	39,501
Securities available for sale	0	0
Securities held to maturity	0	0
Loans held for sale		0
Loans, net	0	0
Derivatives	0	0
Accrued interest receivable	0	0
Financial liabilities:
Certificates of deposit	0	0
Demand and other deposits	5,078,667	3,506,670
FHLB advances	0	195,000
Repurchase agreements	0	0
Subordinated debentures	0	0
Derivatives	0	0
Accrued interest payable	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	0	0
Securities available for sale	466,081	638,291
Securities held to maturity	104,911	135,027
Loans held for sale		0
Loans, net	0	0
Derivatives	59,385	15,437
Accrued interest receivable	1,790	2,181
Financial liabilities:
Certificates of deposit	293,552	308,660
Demand and other deposits	0	0
FHLB advances	222,342	239,622
Repurchase agreements	1,353	999
Subordinated debentures	87,615	81,010
Derivatives	67,341	16,645
Accrued interest payable	328	1,467
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	0	0
Securities available for sale	0	0
Securities held to maturity	0	0
Loans held for sale	10,000	12,643
Loans, net	4,645,937	3,685,770
Derivatives	0	0
Accrued interest receivable	14,033	8,727
Financial liabilities:
Certificates of deposit	0	0
Demand and other deposits	0	0
FHLB advances	0	0
Repurchase agreements	0	0
Subordinated debentures	0	0
Derivatives	0	0
Accrued interest payable	$ 0	$ 0