FAIR VALUE - Summary of Assets and Liabilities measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets measured at fair value on recurring basis
Available for sale securities	$ 638,291	$ 680,886
U.S. Treasury securities
Assets measured at fair value on recurring basis
Available for sale securities	50,822
U.S. GSE securities
Assets measured at fair value on recurring basis
Available for sale securities	4,995	29,050
State and municipal obligations
Assets measured at fair value on recurring basis
Available for sale securities	34,964	40,731
U.S. GSE residential mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	84,691	93,538
U.S. GSE residential collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	277,851	357,777
U.S. GSE commercial mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	13,609	3,508
U.S. GSE commercial collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	104,156	90,638
Other asset backed securities
Assets measured at fair value on recurring basis
Available for sale securities	23,401	23,219
Corporate bonds
Assets measured at fair value on recurring basis
Available for sale securities	43,802	42,425
Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	638,291	680,886
Financial Assets: Derivatives	15,437	6,363
Financial Liabilities:
Financial liabilities: Derivatives	16,645	2,215
Fair Value
Assets measured at fair value on recurring basis
Available for sale securities	638,291	680,886
Financial Assets: Derivatives	15,437	6,363
Financial Liabilities:
Financial liabilities: Derivatives	16,645	2,215
Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets measured at fair value on recurring basis
Available for sale securities	0	0
Financial Assets: Derivatives	0	0
Financial Liabilities:
Financial liabilities: Derivatives	0	0
Significant Other Observable Inputs (Level 2)
Assets measured at fair value on recurring basis
Available for sale securities	638,291	680,886
Financial Assets: Derivatives	15,437	6,363
Financial Liabilities:
Financial liabilities: Derivatives	16,645	2,215
Significant Unobservable Inputs (Level 3)
Assets measured at fair value on recurring basis
Available for sale securities	0	0
Financial Assets: Derivatives	0	0
Financial Liabilities:
Financial liabilities: Derivatives	0	0
Recurring basis | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	638,291	680,886
Recurring basis | Carrying Amount | U.S. Treasury securities
Assets measured at fair value on recurring basis
Available for sale securities	50,822
Recurring basis | Carrying Amount | U.S. GSE securities
Assets measured at fair value on recurring basis
Available for sale securities	4,995	29,050
Recurring basis | Carrying Amount | State and municipal obligations
Assets measured at fair value on recurring basis
Available for sale securities	34,964	40,731
Recurring basis | Carrying Amount | U.S. GSE residential mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	84,691	93,538
Recurring basis | Carrying Amount | U.S. GSE residential collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	277,851	357,777
Recurring basis | Carrying Amount | U.S. GSE commercial mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	13,609	3,508
Recurring basis | Carrying Amount | U.S. GSE commercial collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	104,156	90,638
Recurring basis | Carrying Amount | Other asset backed securities
Assets measured at fair value on recurring basis
Available for sale securities	23,401	23,219
Recurring basis | Carrying Amount | Corporate bonds
Assets measured at fair value on recurring basis
Available for sale securities	43,802	42,425
Recurring basis | Carrying Amount | Derivatives
Assets measured at fair value on recurring basis
Financial Assets: Derivatives	15,437	6,363
Financial Liabilities:
Financial liabilities: Derivatives	16,645	2,215
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value
Assets measured at fair value on recurring basis
Available for sale securities	638,291	680,886
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | U.S. Treasury securities
Assets measured at fair value on recurring basis
Available for sale securities	50,822
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | U.S. GSE securities
Assets measured at fair value on recurring basis
Available for sale securities	4,995	29,050
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | State and municipal obligations
Assets measured at fair value on recurring basis
Available for sale securities	34,964	40,731
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | U.S. GSE residential mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	84,691	93,538
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | U.S. GSE residential collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	277,851	357,777
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | U.S. GSE commercial mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	13,609	3,508
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | U.S. GSE commercial collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	104,156	90,638
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | Other asset backed securities
Assets measured at fair value on recurring basis
Available for sale securities	23,401	23,219
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | Corporate bonds
Assets measured at fair value on recurring basis
Available for sale securities	43,802	42,425
Recurring basis | Significant Other Observable Inputs (Level 2) | Fair Value | Derivatives
Assets measured at fair value on recurring basis
Financial Assets: Derivatives	15,437	6,363
Financial Liabilities:
Financial liabilities: Derivatives	$ 16,645	$ 2,215