INCOME TAXES - Summary of Net Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Allowance for loan losses	$ 10,291	$ 5,207
Operating lease liabilities	3,514	2,137
Effective hedging derivatives	4,543	445
Fair value adjustment on loans	1,037	1,478
Unfunded status of defined benefit plan	7,950	8,540
State business tax credit	362	423
Stock-based compensation	1,105	914
Other	1,776
Gross deferred tax assets	30,578	19,144
Liabilities
Retirement and other benefit plans	1,582	2,179
Premises and equipment	9,057	6,842
Operating lease ROU assets	3,163	2,049
Core deposit intangible	1,385	1,990
Unrealized gains on securities AFS	30,940	10,278
Other		629
Gross deferred tax liabilities	46,127	23,967
Deferred Tax Liabilities, Net	$ 15,549	$ 4,823