Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash	$ 402	$ 5,886	$ 6,299
Retention Accounts
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash	$ 402	386
Letter of guarantee
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash		$ 5,500