Annual report pursuant to Section 13 and 15(d)

Fair Value of Investments (Details)

v3.10.0.1
Fair Value of Investments (Details) - Recurring
$ in Thousands
Dec. 31, 2018
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets $ 105,259
Money market funds  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 12,947
U.S. government securities  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 15,923
Corporate bonds  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 31,495
Commerical paper  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 27,869
Asset-backed securities  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 17,025
Quoted Prices in Active Markets for Identical Assets (Level 1)  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 28,870
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 12,947
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. government securities  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 15,923
Significant Other Observable Inputs (Level 2)  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 76,389
Significant Other Observable Inputs (Level 2) | Corporate bonds  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 31,495
Significant Other Observable Inputs (Level 2) | Commerical paper  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets 27,869
Significant Other Observable Inputs (Level 2) | Asset-backed securities  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Total assets $ 17,025