Financial Instruments - Offsetting of Foreign Currency Derivative Contracts (Details) - Foreign currency exchange contract [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Gross Assets Recognized	$ 736	$ 2,138
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Net Amounts Presented in Condensed Consolidated Balance Sheets	736	2,138
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Financial Instruments	736	0
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Cash Collateral Pledged	0	0
Net Amount	0	2,138
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	5,464	0
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Net Amounts Presented in Condensed Consolidated Balance Sheets	5,464	0
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Financial Instruments	736	0
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Cash Collateral Received	0	0
Net Amount	$ 4,728	$ 0

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