RETIREMENT AND POSTRETIREMENT PLANS - Dime KSOP Plan, BMP and Outside Director Retire - Narratives (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Dime KSOP Plan
Defined Benefit Plan Disclosure [Line Items]
Contribution plan cost		$ 300	$ 1,900	$ 1,900
Dime KSOP Plan | Common stock
Defined Benefit Plan Disclosure [Line Items]
Total Plan Assets		$ 40	33,700
BMP and Outside Director Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Termination age of board members		75 years
Curtailment loss	$ 1,500
BMP and Outside Director Retirement Plan | RETIREMENT PLANS
Defined Benefit Plan Disclosure [Line Items]
Obligation			9,328	$ 9,360
Curtailment loss		$ (1,543)
Benefits paid		9,063	771
Outside Director Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Obligation		2,800
Board Member Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Obligation		$ 6,200
Board Member Retirement Plan | Common stock
Defined Benefit Plan Disclosure [Line Items]
Total Plan Assets			$ 2,200