FAIR VALUE - Summary of Assets and Liabilities measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets measured at fair value on recurring basis
Available for sale securities	$ 466,081	$ 638,291
Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	466,081	638,291
Financial Assets: Derivatives	59,385	15,437
Financial Liabilities:
Financial liabilities: Derivatives	67,341	16,645
Fair Value
Assets measured at fair value on recurring basis
Available for sale securities	466,081	638,291
Financial Assets: Derivatives	59,385	15,437
Financial Liabilities:
Financial liabilities: Derivatives	67,341	16,645
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
State and municipal obligations
Assets measured at fair value on recurring basis
Available for sale securities	36,504	34,964
U.S. GSE residential mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	118,876	84,691
U.S. GSE residential collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	161,582	277,851
U.S. GSE commercial mortgage-backed securities
Assets measured at fair value on recurring basis
Available for sale securities	13,368	13,609
U.S. GSE commercial collateralized mortgage obligations
Assets measured at fair value on recurring basis
Available for sale securities	64,792	104,156
Other asset backed securities
Assets measured at fair value on recurring basis
Available for sale securities	23,894	23,401
Corporate bonds
Assets measured at fair value on recurring basis
Available for sale securities	47,065	43,802
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	466,081	638,291
Financial Assets: Derivatives	59,385	15,437
Financial Liabilities:
Financial liabilities: Derivatives	67,341	16,645
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	466,081	638,291
Recurring basis | U.S. Treasury securities | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities		50,822
Recurring basis | U.S. GSE securities | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities		4,995
Recurring basis | State and municipal obligations | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	36,504	34,964
Recurring basis | U.S. GSE residential mortgage-backed securities | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	118,876	84,691
Recurring basis | U.S. GSE residential collateralized mortgage obligations | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	161,582	277,851
Recurring basis | U.S. GSE commercial mortgage-backed securities | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	13,368	13,609
Recurring basis | U.S. GSE commercial collateralized mortgage obligations | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	64,792	104,156
Recurring basis | Other asset backed securities | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	23,894	23,401
Recurring basis | Corporate bonds | Carrying Amount
Assets measured at fair value on recurring basis
Available for sale securities	47,065	43,802
Recurring basis | Derivatives | Carrying Amount
Assets measured at fair value on recurring basis
Financial Assets: Derivatives	59,385	15,437
Financial Liabilities:
Financial liabilities: Derivatives	67,341	16,645
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets measured at fair value on recurring basis
Available for sale securities	466,081	638,291
Recurring basis | Significant Other Observable Inputs (Level 2) | 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) | U.S. GSE securities
Assets measured at fair value on recurring basis
Available for sale securities		4,995
Recurring basis | Significant Other Observable Inputs (Level 2) | State and municipal obligations
Assets measured at fair value on recurring basis
Available for sale securities	36,504	34,964
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	118,876	84,691
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	161,582	277,851
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	13,368	13,609
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	64,792	104,156
Recurring basis | Significant Other Observable Inputs (Level 2) | Other asset backed securities
Assets measured at fair value on recurring basis
Available for sale securities	23,894	23,401
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate bonds
Assets measured at fair value on recurring basis
Available for sale securities	47,065	43,802
Recurring basis | Significant Other Observable Inputs (Level 2) | Derivatives
Assets measured at fair value on recurring basis
Financial Assets: Derivatives	59,385	15,437
Financial Liabilities:
Financial liabilities: Derivatives	$ 67,341	$ 16,645