Annual report pursuant to Section 13 and 15(d)

Cash, Cash Equivalents and Investments - Cash Equivalents and Investments (Details)

v3.19.1
Cash, Cash Equivalents and Investments - Cash Equivalents and Investments (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Amortized Cost $ 53,379 $ 45,494
Unrealized gains 4 1
Unrealized losses (143) (820)
Fair Value 53,240 44,673
US treasuries    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Amortized Cost 7,541 4,287
Unrealized gains 0 0
Unrealized losses (23) (115)
Fair Value $ 7,518 $ 4,172
US treasuries | Minimum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Contractual maturity 150 days 212 days
US treasuries | Maximum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Contractual maturity 164 days 340 days
Asset-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Amortized Cost $ 5,766 $ 2,709
Unrealized gains 1 0
Unrealized losses (9) (14)
Fair Value $ 5,758 $ 2,695
Asset-backed securities | Minimum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Contractual maturity 196 days 197 days
Asset-backed securities | Maximum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Contractual maturity 259 days 365 days
Asset-backed securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Amortized Cost   $ 3,798
Unrealized gains   0
Unrealized losses   (110)
Fair Value   $ 3,688
Asset-backed securities | Minimum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Contractual maturity   365 days
Corporate bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Amortized Cost $ 40,072 $ 28,356
Unrealized gains 3 0
Unrealized losses (111) (473)
Fair Value $ 39,964 $ 27,882
Corporate bonds | Minimum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Contractual maturity 73 days 91 days
Corporate bonds | Maximum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Contractual maturity 252 days 365 days
Corporate bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Amortized Cost   $ 6,344
Unrealized gains   1
Unrealized losses   (108)
Fair Value   $ 6,236
Corporate bonds | Minimum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Contractual maturity   365 days