Revenue - Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total customer receivables	$ 288,288	$ 298,118
Unbilled receivables	14,752	11,922
Billed receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total customer receivables	$ 273,536	$ 286,196