BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair Value Accounting (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets (liabilities)
Other long-term assets	$ 4,483	$ 4,835
Recurring basis | Level 1
Assets (liabilities)
Pension plan assets	6,347	6,099
Other long-term assets	5,386	4,690
Recurring basis | Level 2
Assets (liabilities)
Interest rate swaps/liabilities	$ (1,889)	$ (363)