Annual report pursuant to Section 13 and 15(d)

FAIR VALUE (Details)

v3.10.0.1
FAIR VALUE (Details) - Fair value measurements recurring - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value $ 125,911 $ 115,169
Money market funds | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 9,106 2,795
U.S. treasury bills | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value   6,726
Government-sponsored enterprises securities | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 7,872 7,826
Corporate bonds and commercial paper | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 108,933 97,822
Fair value inputs Level 1    
Fair Value    
Investments at fair value 9,106 2,795
Fair value inputs Level 1 | Money market funds    
Fair Value    
Investments at fair value 9,106 2,795
Fair value inputs Level 2    
Fair Value    
Investments at fair value 116,805 112,374
Fair value inputs Level 2 | U.S. treasury bills    
Fair Value    
Investments at fair value   6,726
Fair value inputs Level 2 | Government-sponsored enterprises securities    
Fair Value    
Investments at fair value 7,872 7,826
Fair value inputs Level 2 | Corporate bonds and commercial paper    
Fair Value    
Investments at fair value $ 108,933 $ 97,822