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Investments and Fair Value Measurements- Recurring basis (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Assets, Fair Value Disclosure [Abstract] |  |
Investments, amortized cost | $ 23,816 | $ 32,608
Recurring [Member] |  |
Assets, Fair Value Disclosure [Abstract] |  |
Total | 25,563 | 33,350
Recurring [Member] | Certificates of Deposit [Member] |  |
Assets, Fair Value Disclosure [Abstract] |  |
Cash and cash equivalents, fair value disclosure | 7,184 | 7,817
Recurring [Member] | Corporate Bonds [Member] |  |
Assets, Fair Value Disclosure [Abstract] |  |
Investments, amortized cost | 18,379 | 25,533
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Assets, Fair Value Disclosure [Abstract] |  |
Total | 25,563 | 33,350
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Certificates of Deposit [Member] |  |
Assets, Fair Value Disclosure [Abstract] |  |
Cash and cash equivalents, fair value disclosure | 7,184 | 7,817
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member] |  |
Assets, Fair Value Disclosure [Abstract] |  |
Investments, amortized cost | $ 18,379 | $ 25,533

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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. + References No definition available. + Details
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