Quarterly report pursuant to Section 13 or 15(d)

Fair Value (Details)

v3.7.0.1
Fair Value (Details) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Fair Value    
Investments at fair value $ 88,380 $ 65,030
Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 97,586 74,526
U.S. treasury bills    
Fair Value    
Investments at fair value   4,300
Government-sponsored enterprises securities    
Fair Value    
Investments at fair value 11,601 16,459
Corporate bonds and commercial paper    
Fair Value    
Investments at fair value 76,779 44,271
Fair value inputs Level 1    
Fair Value    
Investments at fair value 9,206 9,496
Fair value inputs Level 2    
Fair Value    
Investments at fair value 88,380 65,030
Fair value measurements recurring | Money market funds | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 9,206 9,496
Fair value measurements recurring | U.S. treasury bills | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value   4,300
Fair value measurements recurring | Government-sponsored enterprises securities | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 11,601 16,459
Fair value measurements recurring | Corporate bonds and commercial paper | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 76,779 44,271
Fair value measurements recurring | Fair value inputs Level 1 | Money market funds    
Fair Value    
Investments at fair value 9,206 9,496
Fair value measurements recurring | Fair value inputs Level 2 | U.S. treasury bills    
Fair Value    
Investments at fair value   4,300
Fair value measurements recurring | Fair value inputs Level 2 | Government-sponsored enterprises securities    
Fair Value    
Investments at fair value 11,601 16,459
Fair value measurements recurring | Fair value inputs Level 2 | Corporate bonds and commercial paper    
Fair Value    
Investments at fair value $ 76,779 $ 44,271