Accounting Policies - Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Values of Financial Instruments
Foreign exchange hedges liabilities	$ (11)	$ (16)
Recurring \| Fair value \| Cash flows approach
Fair Values of Financial Instruments
Foreign exchange hedges liabilities	(11)	(16)
Recurring \| Fair value \| Significant Other Observable Inputs (Level 2) \| Cash flows approach
Fair Values of Financial Instruments
Foreign exchange hedges liabilities	$ (11)	$ (16)

Fair value as of the balance sheet date of all foreign currency derivative liabilities designated as cash flow hedging instruments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Name:	us-gaap_ForeignCurrencyCashFlowHedgeLiabilityAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant