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Significant Accounting Policies - Trade Accounts Receivable and Allowance for Credit Losses (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]    
Receivables related to contracts with customers $ 145,929 $ 133,480
Other receivables 4,238 13,679
Trade Receivables    
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Allowance for Credit Losses, Beginning of Period 0 0
Provision for Expected Credit Losses 84 0
Allowance for Credit Losses, End of Period 84 0
Other Receivables    
Accounts Receivable, Allowance for Credit Loss [Roll Forward]    
Allowance for Credit Losses, Beginning of Period 2,463 2,038
Provision for Expected Credit Losses 2,760 595
Write-off of Uncollectible Accounts (1,975) (170)
Allowance for Credit Losses, End of Period $ 3,248 $ 2,463