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Fair Value Measurements (Detail Textuals) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]        
Cash and cash equivalents, primarily include money market funds $ 48,963 $ 51,608 $ 49,125 $ 51,913
Fair value on recurring basis | Money market funds (included in cash and cash equivalents) | Fair Value Measurement, Quoted Prices in Active Markets for Identical Assets (Level 1)        
Schedule of Available-for-sale Securities [Line Items]        
Cash equivalents, primarily include money market funds $ 47,800 $ 50,000