Receivables - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 7,580	$ 7,225
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 6,600	$ 6,300