Receivables (Details Textual) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 11,299		$ 11,567
Receivables, net	267,179	$ 257,425	265,866
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 10,400		10,800
ASU 2014-09 | Difference between revenue guidance in effect before and after Topic 606
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables, net			$ (8,400)