Revenue - Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total customer receivables	$ 298,118	$ 313,719
Unbilled receivables	11,922	14,492
Billed receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total customer receivables	$ 286,196	$ 299,227