INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Allowance for loan losses and off-balance sheet credit exposure	$ 10,305	$ 9,309
Net unrealized losses on securities	343	4,810
Compensation and related benefit obligations	2,368	2,427
Purchase accounting fair value adjustments	4,735	4,141
Net change in pension and other post-retirement benefits plans	2,809	2,630
Net operating loss carryforward	3,229	4,746
Net loss on cash flow hedges	304
Operating lease liabilities	13,444
Other	200	671
Total deferred tax assets	37,737	28,734
Deferred tax liabilities:
Pension and SERP expense	(4,904)	(4,559)
Depreciation	(956)	(1,163)
REIT undistributed net income	(2,403)	(2,110)
Net deferred loan costs and fees	(2,413)	(2,206)
Net gain on cash flow hedges		(1,210)
State and local taxes	(1,227)	(1,468)
Operating lease right-of-use assets	(12,934)
Other	(835)	(353)
Total deferred tax liabilities	(25,672)	(13,069)
Net deferred tax asset	$ 12,065	$ 15,665