FAIR VALUE - Summary of Estimated Fair Values and Carrying Amounts of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019
Financial assets:
Cash and due from banks	$ 61,352	$ 77,693
Interest-bearing deposits with banks	172,830	39,501
Securities available for sale	553,278	638,291
Securities held to maturity	127,653	135,027
Accrued interest receivable	11,070	10,908
Carrying Amount
Financial assets:
Cash and due from banks	61,352	77,693
Interest-bearing deposits with banks	172,830	39,501
Securities available for sale	553,278	638,291
Securities restricted	26,354	32,879
Securities held to maturity	124,231	133,638
Loans held for sale	12,643	12,643	$ 12,600
Loans, net	3,722,915	3,647,499
Derivatives	57,874	15,437
Accrued interest receivable	11,070	10,908
Financial liabilities:
Certificates of deposit	310,077	307,977
Demand and other deposits	3,745,658	3,506,670
FHLB advances	290,000	435,000
Repurchase agreements	1,195	999
Subordinated debentures	78,955	78,920
Derivatives	68,839	16,645
Accrued interest payable	387	1,467
Fair Value
Financial assets:
Cash and due from banks	61,352	77,693
Interest-bearing deposits with banks	172,830	39,501
Securities available for sale	553,278	638,291
Securities held to maturity	127,653	135,027
Loans held for sale	12,643	12,643
Loans, net	3,755,669	3,685,770
Derivatives	57,874	15,437
Accrued interest receivable	11,070	10,908
Financial liabilities:
Certificates of deposit	312,965	308,660
Demand and other deposits	3,745,658	3,506,670
FHLB advances	300,760	434,622
Repurchase agreements	1,195	999
Subordinated debentures	89,678	81,010
Derivatives	68,839	16,645
Accrued interest payable	387	1,467
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and due from banks	61,352	77,693
Interest-bearing deposits with banks	172,830	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	3,745,658	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	553,278	638,291
Securities held to maturity	127,653	135,027
Loans held for sale		0
Loans, net	0	0
Derivatives	57,874	15,437
Accrued interest receivable	2,105	2,181
Financial liabilities:
Certificates of deposit	312,965	308,660
Demand and other deposits	0	0
FHLB advances	300,760	239,622
Repurchase agreements	1,195	999
Subordinated debentures	89,678	81,010
Derivatives	68,839	16,645
Accrued interest payable	387	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	12,643	12,643
Loans, net	3,755,669	3,685,770
Derivatives	0	0
Accrued interest receivable	8,965	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