Cash and Cash Equivalents, and Long Term Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 73,636	$ 56,689	$ 53,539
Long term restricted cash included in other assets	520		537
Cash, cash equivalents and long term restricted cash shown in the consolidated statement of cash flows	$ 74,156		$ 54,076

Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. 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_RestrictedCashAndCashEquivalentsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant