Quarterly report pursuant to Section 13 or 15(d)

Short Term Investments - Schedule of Available for Sale Short-term Investments by Major Security Types (Details)

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Short Term Investments - Schedule of Available for Sale Short-term Investments by Major Security Types (Details)
$ in Thousands
Dec. 31, 2018
USD ($)
Schedule Of Available For Sale Securities [Line Items]  
Available for sale, Cost Total $ 39,722
Available for sale, Unrealized gains 287
Available for sale, Unrealized (losses) (9)
Available for sale, Fair Value Total 40,000
Available for sale, Maturity by period Less than 1 year 40,000
Commercial Paper  
Schedule Of Available For Sale Securities [Line Items]  
Available for sale, Cost Total 35,745
Available for sale, Unrealized gains 272
Available for sale, Unrealized (losses) (9)
Available for sale, Fair Value Total 36,008
Available for sale, Maturity by period Less than 1 year 36,008
U.S. Treasury and Agency Bonds  
Schedule Of Available For Sale Securities [Line Items]  
Available for sale, Cost Total 3,977
Available for sale, Unrealized gains 15
Available for sale, Fair Value Total 3,992
Available for sale, Maturity by period Less than 1 year $ 3,992