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Revenue - Change in Contract Balances (Details)
$ in Thousands
 9 Months Ended
Sep. 30, 2021
USD ($)
Contract Assets  
Contract with customer, asset, net, beginning balance $ 26,780
Payments received for services billed in prior period (26,780)
Services provided and billed in current period 176,264
Payments received for services billed in current period (156,465)
Contract with customer, asset, net, ending balance 19,799
Contract Liabilities  
Contract with customer, liability, beginning balance (22,856)
Amortization of deferred commissioning period revenue 3,081
Contract with customer, liability, ending balance $ (19,775)