DEBT - Summary of Long-term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Apr. 20, 2020	Jan. 31, 2019
Debt Instruments
Other	$ 110	$ 141
Total long-term debt, including current maturities	77,746	88,143
Less current maturities	(3,404)	(6,791)
Total long-term debt	74,342	81,352
Revolving credit agreement
Debt Instruments
Total long-term debt, including current maturities	66,900	73,025	$ 170,000	$ 225,000
Sale-leaseback finance obligations
Debt Instruments
Total long-term debt, including current maturities	9,082	9,913
Insurance premium financing (2020)
Debt Instruments
Total long-term debt, including current maturities	$ 1,654	$ 5,064