PENSION AND OTHER POSTRETIREMENT PLANS - Financial Assets Measured At Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Employee benefits
Total plan assets	$ 44,060	$ 39,745	$ 33,874
Carrying Amount | Recurring basis
Employee benefits
Total plan assets	44,060	39,745
Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	26,876	25,050
Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	17,184	14,695
Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
Cash and cash equivalents | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	2,452	1,444
Cash and cash equivalents | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	0	0
Cash and cash equivalents | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	2,452	1,444
Cash and cash equivalents | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
Equity Securities | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	25,023	23,026
Equity Securities | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	25,023	23,026
Equity Securities | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	0	0
Equity Securities | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
U.S. large cap | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	15,449	12,097
U.S. large cap | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	15,449	12,097
U.S. large cap | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	0	0
U.S. large cap | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
U.S. Mid cap/small cap | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	3,471	4,195
U.S. Mid cap/small cap | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	3,471	4,195
U.S. Mid cap/small cap | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	0	0
U.S. Mid cap/small cap | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
International | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	6,029	6,320
International | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	6,029	6,320
International | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	0	0
International | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
Equities blend | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	74	414
Equities blend | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	74	414
Equities blend | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	0	0
Equities blend | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
Fixed income securities | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	16,585	15,275
Fixed income securities | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	1,853	2,024
Fixed income securities | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	14,732	13,251
Fixed income securities | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
Corporate | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	1,853	2,024
Corporate | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	1,853	2,024
Corporate | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	0	0
Corporate | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
Government | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	2,342	2,926
Government | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	0	0
Government | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	2,342	2,926
Government | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
Mortgage-backed | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	2,325	1,033
Mortgage-backed | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	0	0
Mortgage-backed | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	2,325	1,033
Mortgage-backed | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	0	0
High yield bonds and bond funds | Carrying Amount | Recurring basis
Employee benefits
Total plan assets	10,065	9,292
High yield bonds and bond funds | Quoted Prices In Active Markets for Identical Assets (Level 1) | Recurring basis
Employee benefits
Total plan assets	0	0
High yield bonds and bond funds | Significant Other Observable Inputs (Level 2) | Recurring basis
Employee benefits
Total plan assets	10,065	9,292
High yield bonds and bond funds | Significant Unobservable Inputs (Level 3) | Recurring basis
Employee benefits
Total plan assets	$ 0	$ 0