Summary of Significant Accounting Policies, Derivative Instruments, Fair Values Derivatives, Balance Sheet Location (Details) - Foreign Exchange Contract [Member] - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Estimated fair value of the contracts in the consolidated balance sheets [Abstract]
Asset derivatives	$ 201	$ 141
Liability derivatives	0	20
Net fair value	201	121
Prepaid Expenses and Other Current Assets [Member]
Estimated fair value of the contracts in the consolidated balance sheets [Abstract]
Asset derivatives	201	57
Other Assets [Member]
Estimated fair value of the contracts in the consolidated balance sheets [Abstract]
Asset derivatives	0	84
Other Current Liabilities [Member]
Estimated fair value of the contracts in the consolidated balance sheets [Abstract]
Liability derivatives	$ 0	$ 20