Quarterly report pursuant to Section 13 or 15(d)

Fair Value (Details)

v3.19.3
Fair Value (Details) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Fair Value    
Investments at fair value $ 78,930 $ 116,805
Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 105,845 125,911
U.S. treasury bills    
Fair Value    
Investments at fair value 8,045  
Government-sponsored enterprises securities    
Fair Value    
Investments at fair value 15,165 7,872
Corporate bonds and commercial paper    
Fair Value    
Investments at fair value 55,720 108,933
Fair value inputs Level 1    
Fair Value    
Investments at fair value 26,915 9,106
Fair value inputs Level 2    
Fair Value    
Investments at fair value 78,930 116,805
Fair value measurements recurring | Money market funds | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 26,915 9,106
Fair value measurements recurring | U.S. treasury bills | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 8,045  
Fair value measurements recurring | Government-sponsored enterprises securities | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 15,165 7,872
Fair value measurements recurring | Corporate bonds and commercial paper | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 55,720 108,933
Fair value measurements recurring | Fair value inputs Level 1 | Money market funds    
Fair Value    
Investments at fair value 26,915 9,106
Fair value measurements recurring | Fair value inputs Level 2 | U.S. treasury bills    
Fair Value    
Investments at fair value 8,045  
Fair value measurements recurring | Fair value inputs Level 2 | Government-sponsored enterprises securities    
Fair Value    
Investments at fair value 15,165 7,872
Fair value measurements recurring | Fair value inputs Level 2 | Corporate bonds and commercial paper    
Fair Value    
Investments at fair value $ 55,720 $ 108,933