Revenue - Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total customer receivables	$ 318,057	$ 313,719
Unbilled receivables	10,877	14,492
Billed receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total customer receivables	$ 307,180	$ 299,227

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant