BORROWINGS (Trust Preferred Securities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Junior Subordinated Debentures [Member]
Debt Instrument [Line Items]
Face Amount	$ 61.0	$ 61.0
Junior Subordinated Debentures [Member] | Capital Trust V Preferred Securities Due in 2037 [Member]
Debt Instrument [Line Items]
Face Amount	$ 50.0
Fixed rate	1.70%
Junior Subordinated Debentures [Member] | Capital Trust V Preferred Securities Due in 2037 [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.48%
Junior Subordinated Debentures [Member] | Central Bancorp Capital Trust I Securities Due in 2034 [Member]
Debt Instrument [Line Items]
Face Amount	$ 5.1
Basis spread on variable rate	2.66%
Junior Subordinated Debentures [Member] | Central Bancorp Capital Trust I Securities Due in 2034 [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	2.44%
Junior Subordinated Debentures [Member] | Central Bancorp Capital Trust II Securities Due in 2037 [Member]
Debt Instrument [Line Items]
Face Amount	$ 5.9
Junior Subordinated Debentures [Member] | Central Bancorp Capital Trust II Securities Due in 2037 [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.65%
Fixed rate	1.87%
Subordinated Debt [Member] | Subordinated Debentures Due in November 2019 [Member] [Domain]
Debt Instrument [Line Items]
Fixed rate		4.75%