Quarterly report pursuant to Section 13 or 15(d)

Short-term Investments (Details)

v3.10.0.1
Short-term Investments (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]    
Amortized Cost $ 33,408 $ 32,424
Unrealized Gains 11 74
Unrealized Losses (12) (79)
Fair Value 33,407 32,419
Commercial paper    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized Cost 8,955 11,962
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 8,955 11,962
Overnight repurchase agreement    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized Cost 9,500 9,000
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 9,500 9,000
U.S. government securities    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized Cost 14,953 11,462
Unrealized Gains 11 74
Unrealized Losses (12) (79)
Fair Value $ 14,952 $ 11,457