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Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | $ 8,953 | $ 48,818
Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 48,593 | 73,404
Common stock warrant liability |  | 15
Total financial liabilities |  | 15
Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 27,641 | 24,586
Common stock warrant liability |  | 0
Total financial liabilities |  | 0
Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 20,952 | 48,818
Common stock warrant liability |  | 0
Total financial liabilities |  | 0
Fair Value, Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total financial assets | 0 | 0
Common stock warrant liability |  | 15
Total financial liabilities |  | 15
Commercial paper | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 6,497 | 15,991
Commercial paper | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
Commercial paper | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 6,497 | 15,991
Commercial paper | Fair Value, Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
Corporate notes/bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 1,205 | 29,296
Corporate notes/bonds | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 1,205 | 29,296
Corporate notes/bonds | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
Corporate notes/bonds | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 1,205 | 29,296
Corporate notes/bonds | Fair Value, Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
U.S. Treasuries |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: |  | 2,253
U.S. Treasuries | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: |  | 2,253
U.S. Treasuries | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: |  | 0
U.S. Treasuries | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: |  | 2,253
U.S. Treasuries | Fair Value, Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: |  | 0
U.S. Government agency securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 1,251 | 1,278
U.S. Government agency securities | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 1,251 | 1,278
U.S. Government agency securities | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
U.S. Government agency securities | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 1,251 | 1,278
U.S. Government agency securities | Fair Value, Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
Money market funds | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 27,641 | 24,586
Money market funds | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 27,641 | 24,586
Money market funds | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Money market funds | Fair Value, Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | $ 0
Corporate notes/bonds | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 2,000 |
Corporate notes/bonds | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 |
Corporate notes/bonds | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 2,000 |
Corporate notes/bonds | Fair Value, Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 |
U.S. Treasuries | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 9,999 |
U.S. Treasuries | Fair Value, Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 |
U.S. Treasuries | Fair Value, Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 9,999 |
U.S. Treasuries | Fair Value, Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | $ 0 |

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563 + Details
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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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- Definition Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities. + References No definition available. + Details
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