Quarterly report pursuant to Section 13 or 15(d)

Cash Equivalents and Marketable Securities (Details)

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Cash Equivalents and Marketable Securities (Details)
 9 Months Ended
Sep. 30, 2019
USD ($)
item
Dec. 31, 2018
USD ($)
Cash Equivalents and Marketable Securities    
Marketable Securities, Amortized Cost $ 108,117,000 $ 99,682,000
Marketable Securities, Unrealized Gains 21,000  
Marketable Securities, Unrealized Losses   (3,000)
Marketable Securities, Fair Value 108,138,000 99,679,000
Realized gains (losses) $ 0  
Number of investments adjusted for other-than-temporary declines in fair value | item 0  
Fair value of securities held by Company in an unrealized loss position for less than twelve months $ 10,000,000  
Number of securities in unrealized loss position for more than twelve months | item 0  
Number of securities with an other-than-temporary impairment | item 0  
Number of securities in unrealized loss position for less than twelve months | item 2  
U.S treasury obligations    
Cash Equivalents and Marketable Securities    
Marketable Securities, Amortized Cost $ 74,753,000 49,796,000
Marketable Securities, Unrealized Gains 21,000  
Marketable Securities, Unrealized Losses   (3,000)
Marketable Securities, Fair Value 74,774,000 49,793,000
Cash and money market funds    
Cash Equivalents and Marketable Securities    
Cash Equivalents, Amortized Cost 21,364,000 34,886,000
Cash Equivalents, Fair value 21,364,000 34,886,000
Overnight repurchase agreements    
Cash Equivalents and Marketable Securities    
Cash Equivalents, Amortized Cost 12,000,000 15,000,000
Cash Equivalents, Fair value $ 12,000,000 $ 15,000,000