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OPERATING REVENUES - Narrative (Details) - USD ($)
$ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]    
Contract assets $ 82,192 $ 62,958
Impairment loss 0 $ 0
Balance Capitalized In Current Year    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Gross asset contract with customer 5,200  
Amortization capitalized contract cost 1,900  
Contract assets 3,300  
Balance Capitalized In Prior Year    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Amortization capitalized contract cost $ 2,500