Derivatives - Fair value of derivative instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Interest rate swap contract \| Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Derivative liabilities	$ 363	$ 372
Interest rate swap contract \| Derivatives Designated as Hedging Instruments \| Prepaids and other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	291	134
Interest rate swap contract \| Derivatives Designated as Hedging Instruments \| Other assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	72	238
Foreign currency forward contracts \| Not Designated as Hedging Instrument \| Prepaids and other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	$ 240	$ 390

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

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