STOCKHOLDERS' EQUITY - Reclass (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Unrecognized Net Periodic Benefit Credit (costs)
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax	$ 501	$ (9,725)
Tax benefit (expense)	(129)	1,481
Total, net of tax	372	(8,244)
Unrecognized Net Periodic Benefit Credit (costs) | Nonunion Defined Benefit Pension Plan
Significant reclassifications out of accumulated other comprehensive loss by component
Total, net of tax		(7,300)
Amortization of net actuarial gain (loss)
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax	589	(1,253)
Amortization of net actuarial gain (loss) | Nonunion Defined Benefit Pension Plan
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax		(300)
Amortization of prior service credit
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax	1	33
Pension settlement expense, including termination expense
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax	$ (89)	(8,505)
Pension settlement expense, including termination expense | Nonunion Defined Benefit Pension Plan
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax		(8,100)
Pension termination expense | Nonunion Defined Benefit Pension Plan
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax		(4,000)
Tax benefit (expense)		$ 0