RETIREMENT AND POSTRETIREMENT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Retirement and Postretirement Plans [Abstract]
Curtailment loss				$ 1,543
Distributions to Retired Participants [Abstract]
Defined contribution plan description				100% of each employee’s contributions up to 1% of each employee’s compensation plus 50% of each employee’s contributions over 1% but not in excess of 6% of each employee’s compensation for a maximum contribution of 3.5% of a participating employee’s compensation.
Minimum employee contribution percentage				1.00%
Percentage of employer matching contribution				50.00%
Threshold limit percentage of employee compensation				6.00%
Maximum percentage of annual contribution per employee				3.50%
Cash				$ 9,200
Market value of Common Stock from Employee Stock Ownership Plan of BMP (000 shares)				$ 2,400
Returned to treasury Stock				41,101
Gross lump-sum distribution		$ 11,600
Non-cash tax benefit				$ 301
Distribution of common stock (in shares)				88,081
BMP Retirement Plan
Retirement and Postretirement Plans [Abstract]
Planned contributions/benefit payments	$ 0			$ 0
Retirement Plans [Member] | BMP Retirement Plan
Net Periodic Benefit Cost [Abstract]
Service cost	223			594
Interest cost	302			854
Expected return on assets	(1,244)			(3,473)
Amortization of unrealized loss	207			619
Net periodic (credit) cost	(512)			(1,406)
Retirement Plans [Member] | Employee Retirement Plan [Member]
Net Periodic Benefit Cost [Abstract]
Interest cost	183		$ 10	549	$ 30
Expected return on assets	(428)			(1,284)
Unrecognized past service liability			(2)		(6)
Amortization of unrealized loss	229			687
Net periodic (credit) cost	(16)		8	(48)	24
Retirement Plans [Member] | BMP, Postretirement And Outside Director Retirement Plans
Net Periodic Benefit Cost [Abstract]
Interest cost			241		723
Expected return on assets			(428)		(1,284)
Amortization of unrealized loss			274		822
Net periodic (credit) cost			$ 87		$ 261
Retirement Plans [Member] | BMP, Employee and Outside Director Retirement Plans [Member]
Retirement and Postretirement Plans [Abstract]
Planned contributions/benefit payments	$ 2,800			2,800
Actual contributions/benefit payments				$ 6,200
Curtailment loss		$ 1,500