FAIR VALUE - Summary of Assets and Liabilities measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets measured at fair value on recurring basis
Available for sale securities	$ 707,451	$ 680,886
U.S. GSE securities
Assets measured at fair value on recurring basis
Available for sale securities	39,475	29,050
State and municipal obligations
Assets measured at fair value on recurring basis
Available for sale securities	43,165	40,731
U.S. GSE residential mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	96,612	93,538
U.S. GSE residential collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	364,936	357,777
U.S. GSE commercial mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	7,055	3,508
U.S. GSE commercial collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	90,403	90,638
Other asset backed securities
Assets measured at fair value on recurring basis
Available for sale securities	23,098	23,219
Corporate bonds
Assets measured at fair value on recurring basis
Available for sale securities	42,707	42,425
Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	707,451	680,886
Financial Assets: Derivatives	7,663	6,363
Financial Liabilities:
Financial liabilities: Derivatives	5,772	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	707,451	680,886
Financial Assets: Derivatives	7,663	6,363
Financial Liabilities:
Financial liabilities: Derivatives	5,772	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	707,451	680,886
Recurring basis | Carrying Amount | U.S. GSE securities
Assets measured at fair value on recurring basis
Available for sale securities	39,475	29,050
Recurring basis | Carrying Amount | State and municipal obligations
Assets measured at fair value on recurring basis
Available for sale securities	43,165	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	96,612	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	364,936	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	7,055	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	90,403	90,638
Recurring basis | Carrying Amount | Other asset backed securities
Assets measured at fair value on recurring basis
Available for sale securities	23,098	23,219
Recurring basis | Carrying Amount | Corporate bonds
Assets measured at fair value on recurring basis
Available for sale securities	42,707	42,425
Recurring basis | Carrying Amount | Derivatives
Assets measured at fair value on recurring basis
Financial Assets: Derivatives	7,663	6,363
Financial Liabilities:
Financial liabilities: Derivatives	5,772	2,215
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets measured at fair value on recurring basis
Available for sale securities	707,451	680,886
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. GSE securities
Assets measured at fair value on recurring basis
Available for sale securities	39,475	29,050
Recurring basis | Significant Other Observable Inputs (Level 2) | State and municipal obligations
Assets measured at fair value on recurring basis
Available for sale securities	43,165	40,731
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. GSE residential mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	96,612	93,538
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. GSE residential collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	364,936	357,777
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. GSE commercial mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	7,055	3,508
Recurring basis | Significant Other Observable Inputs (Level 2) | U.S. GSE commercial collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	90,403	90,638
Recurring basis | Significant Other Observable Inputs (Level 2) | Other asset backed securities
Assets measured at fair value on recurring basis
Available for sale securities	23,098	23,219
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate bonds
Assets measured at fair value on recurring basis
Available for sale securities	42,707	42,425
Recurring basis | Significant Other Observable Inputs (Level 2) | Derivatives
Assets measured at fair value on recurring basis
Financial Assets: Derivatives	7,663	6,363
Financial Liabilities:
Financial liabilities: Derivatives	$ 5,772	$ 2,215