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)
$ in Thousands
 6 Months Ended
Jun. 30, 2017
USD ($)
item
Dec. 31, 2016
USD ($)
Cash Equivalents and Marketable Securities    
Marketable Securities, Unrealized Losses $ (6) $ (9)
Total, Amortized Cost 91,527 83,602
Total, Fair Value 91,521 83,593
Realized gains (losses) $ 0  
Number of investments adjusted for other-than-temporary declines in fair value | item 0  
Unrealized Loss Position    
Number of securities in unrealized loss position for less than twelve months | item 4  
Fair value of securities held by Company in an unrealized loss position for less than twelve months $ 10,000  
Number of securities in unrealized loss position for more than twelve months | item 0  
Money market funds    
Cash Equivalents and Marketable Securities    
Cash Equivalents, Amortized Cost $ 32,530 58,588
Cash Equivalents, Fair value 32,530 58,588
Overnight repurchase agreements    
Cash Equivalents and Marketable Securities    
Cash Equivalents, Amortized Cost 47,001  
Cash Equivalents, Fair value 47,001  
U.S treasury obligations    
Cash Equivalents and Marketable Securities    
Marketable Securities, Amortized Cost 11,996 25,014
Marketable Securities, Unrealized Losses (6) (9)
Marketable Securities, Fair Value $ 11,990 $ 25,005