Revenue - Receivables (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total customer receivables	$ 272,387	$ 298,118
Unbilled receivables	11,139	11,922
Billed receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total customer receivables	$ 261,248	$ 286,196