Annual report pursuant to Section 13 and 15(d)

FAIR VALUE (Details)

v3.7.0.1
FAIR VALUE (Details) - Fair value measurements recurring - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value $ 74,526 $ 124,158
Money market funds | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 9,496 26,291
U.S. treasury bills | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 4,300 9,048
Government-sponsored enterprises securities | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 16,459 48,613
Corporate bonds and commercial paper | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 44,271 40,206
Fair value inputs Level 1    
Fair Value    
Investments at fair value 9,496 26,291
Fair value inputs Level 1 | Money market funds    
Fair Value    
Investments at fair value 9,496 26,291
Fair value inputs Level 2    
Fair Value    
Investments at fair value 65,030 97,867
Fair value inputs Level 2 | U.S. treasury bills    
Fair Value    
Investments at fair value 4,300 9,048
Fair value inputs Level 2 | Government-sponsored enterprises securities    
Fair Value    
Investments at fair value 16,459 48,613
Fair value inputs Level 2 | Corporate bonds and commercial paper    
Fair Value    
Investments at fair value $ 44,271 $ 40,206