Cash Equivalents and Investments (Details) - USD ($) $ in Thousands |
Dec. 31, 2018 |
Dec. 31, 2017 |
---|---|---|
Debt Securities, Available-for-sale [Line Items] | ||
Cost | $ 171,784 | $ 236,744 |
Gross unrealized gain | 5 | 0 |
Gross unrealized loss | (13) | 0 |
Fair value | 171,776 | 236,744 |
Short-term investments | 102,556 | 0 |
Money market funds | ||
Debt Securities, Available-for-sale [Line Items] | ||
Cost | 38,354 | 236,744 |
Gross unrealized gain | 0 | 0 |
Gross unrealized loss | 0 | 0 |
Fair value | 38,354 | 236,744 |
US treasury securities | ||
Debt Securities, Available-for-sale [Line Items] | ||
Cost | 80,844 | 0 |
Gross unrealized gain | 5 | 0 |
Gross unrealized loss | (5) | 0 |
Fair value | 80,844 | 0 |
U.S. government agency obligations | ||
Debt Securities, Available-for-sale [Line Items] | ||
Cost | 52,586 | 0 |
Gross unrealized gain | 0 | 0 |
Gross unrealized loss | (8) | 0 |
Fair value | 52,578 | 0 |
Cash equivalents | ||
Debt Securities, Available-for-sale [Line Items] | ||
Fair value | $ 69,220 | $ 236,744 |