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Revenue Recognition (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Research and Development Arrangements [Line Items] |  |  |  |
Development revenue recognized | $ 302 | $ 899 | $ 1,039 | $ 1,816
Customer Concentration Risk [Member] | Revenue Recognized [Member] |  |  |  |
Research and Development Arrangements [Line Items] |  |  |  |
Concentration risk percentage | 53.00% | 53.00% | 53.00% | 53.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member] |  |  |  |
Research and Development Arrangements [Line Items] |  |  |  |
Concentration risk percentage |  |  | 100.00% | 100.00%

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- Definition Aggregate revenue earned during the period from recognition of related party deferred revenue, non-product related activities and revenue earned during the period from non-repayable sum of money awarded to an entity to carry out a specific purpose as provided in grant agreements. + References No definition available. + Details
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