| Cash, Cash Equivalents and Investments [Table Text Block] |
| | | As of December 31, 2021 | |
| | | Amortized Cost | | | Gross Unrealized
Gains | | | Gross Unrealized
Losses | | | Fair
Value | |
| Cash and cash equivalents: | | | | | | | | | | | | | | | | |
| Cash | | $ | 1,443 | | | $ | — | | | $ | — | | | $ | 1,443 | |
| Money market funds | | | 2,822 | | | | — | | | | — | | | | 2,822 | |
| Commercial paper | | | 8,398 | | | | — | | | | — | | | | 8,398 | |
| Total cash and cash equivalents | | | 12,663 | | | | — | | | | — | | | | 12,663 | |
| | | | | | | | | | | | | | | | | |
| Short-term investments: | | | | | | | | | | | | | | | | |
| Commercial paper | | | 29,504 | | | | — | | | | — | | | | 29,504 | |
| Corporate debt securities | | | 9,463 | | | | — | | | | — | | | | 9,463 | |
| Total short-term investments | | | 38,967 | | | | — | | | | — | | | | 38,967 | |
| Total cash, cash equivalents and short-term investments | | $ | 51,630 | | | $ | — | | | $ | — | | | $ | 51,630 | |
| | | As of December 31, 2020 | |
| | | Amortized Cost | | | Gross Unrealized
Gains | | | Gross Unrealized
Losses | | | Fair
Value | |
| Cash and cash equivalents: | | | | | | | | | | | | | | | | |
| Cash | | $ | 5,181 | | | $ | — | | | $ | — | | | $ | 5,181 | |
| Money market funds | | | 3,996 | | | | — | | | | — | | | | 3,996 | |
| Commercial paper | | | 18,097 | | | | — | | | | — | | | | 18,097 | |
| Total cash and cash equivalents | | | 27,274 | | | | — | | | | — | | | | 27,274 | |
| | | | | | | | | | | | | | | | | |
| Short-term investments: | | | | | | | | | | | | | | | | |
| U.S. government agency securities | | | 5,818 | | | | — | | | | — | | | | 5,818 | |
| Commercial paper | | | 9,794 | | | | — | | | | — | | | | 9,794 | |
| Total short-term investments | | | 15,612 | | | | — | | | | — | | | | 15,612 | |
| Total cash, cash equivalents and short-term investments | | $ | 42,886 | | | $ | — | | | $ | — | | | $ | 42,886 | |
|
| Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] |
| | | As of December 31, 2021 | |
| | | Fair Value | | | Level I | | | Level II | | | Level III | |
| Assets | | | | | | | | | | | | | | | | |
| Money market funds | | $ | 2,822 | | | $ | 2,822 | | | $ | — | | | $ | — | |
| Commercial paper | | | 37,902 | | | | — | | | | 37,902 | | | | — | |
| Corporate debt securities | | | 9,463 | | | | — | | | | 9,463 | | | | — | |
| Total assets measured at fair value | | $ | 50,187 | | | $ | 2,822 | | | $ | 47,365 | | | $ | — | |
| | | | | | | | | | | | | | | | | |
| Liabilities | | | | | | | | | | | | | | | | |
| Contingent put option liability | | $ | 81 | | | $ | — | | | $ | — | | | $ | 81 | |
| Total liabilities measured at fair value | | $ | 81 | | | $ | — | | | $ | — | | | $ | 81 | |
| | | As of December 31, 2020 | |
| | | Fair Value | | | Level I | | | Level II | | | Level III | |
| Assets | | | | | | | | | | | | | | | | |
| Money market funds | | $ | 3,996 | | | $ | 3,996 | | | $ | — | | | $ | — | |
| U.S. government agency securities | | | 5,818 | | | | — | | | | 5,818 | | | | — | |
| Commercial paper | | | 27,891 | | | | — | | | | 27,891 | | | | — | |
| Total assets measured at fair value | | $ | 37,705 | | | $ | 3,996 | | | $ | 33,709 | | | $ | — | |
| | | | | | | | | | | | | | | | | |
| Liabilities | | | | | | | | | | | | | | | | |
| Contingent put option liability | | $ | 246 | | | $ | — | | | $ | — | | | $ | 246 | |
| Total liabilities measured at fair value | | $ | 246 | | | $ | — | | | $ | — | | | $ | 246 | |
|