SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Allowance for Credit Losses (Details) - USD ($) $ in Millions  | 
6 Months Ended | |
|---|---|---|
Jun. 30, 2020  | 
Jun. 30, 2019  | 
|
| Accounts Receivable, Allowance for Credit Loss [Roll Forward] | ||
| Allowance for credit losses as of beginning of period | $ 0.0 | $ 0.0 | 
| Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease) | 4.3 | 0.0 | 
| Allowance for credit losses as of end of period | $ 4.3 | $ 0.0 | 
| X | ||||||||||
- Definition Amount of allowance for credit loss on accounts receivable. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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| X | ||||||||||
- Definition Amount of increase (decrease) in allowance for credit loss on accounts receivable. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef 
  | 
| X | ||||||||||
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available. 
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