Annual report pursuant to Section 13 and 15(d)

Cash, Cash Equivalents and Investments - Cash Equivalents and Investments Carried at Fair Value (Details)

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Cash, Cash Equivalents and Investments - Cash Equivalents and Investments Carried at Fair Value (Details)
$ in Thousands
Dec. 31, 2017
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Money market funds, included in cash equivalents $ 4,583
Corporate bonds, included in cash equivalents 13,595
Investments - U.S. treasuries 4,172
Investments - Asset-backed securities 6,384
Investments - Corporate bonds 34,117
Total 62,851
Quoted prices in active markets (Level 1)  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Money market funds, included in cash equivalents 4,583
Corporate bonds, included in cash equivalents
Investments - U.S. treasuries 4,172
Investments - Asset-backed securities
Investments - Corporate bonds
Total 8,755
Significant other observable inputs (Level 2)  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Money market funds, included in cash equivalents
Corporate bonds, included in cash equivalents 13,595
Investments - U.S. treasuries
Investments - Asset-backed securities 6,384
Investments - Corporate bonds 34,117
Total 54,096
Significant unobservable inputs (Level 3)  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Money market funds, included in cash equivalents 0
Corporate bonds, included in cash equivalents 0
Investments - U.S. treasuries 0
Investments - Asset-backed securities 0
Investments - Corporate bonds 0
Total $ 0