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LONG-TERM DEBT AND OTHER FINANCING ARRANGEMENTS 2023 revolving credit facility, narrative (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Mar. 31, 2020
2023 Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Long-term Line of Credit, Noncurrent   $ 0
Line of credit facility, maximum borrowing capacity   $ 75,000
2023 Revolving Credit Facility [Member] | Eurodollar [Member]    
Debt Instrument [Line Items]    
Derivative, Basis Spread on Variable Rate   1.00%
CME NV and CME BV [Member]    
Debt Instrument [Line Items]    
Outstanding Shares Pledged, Percentage   100.00%
CME NV and CME BV [Member] | 2023 Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Outstanding Shares Pledged, Percentage 100.00%