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Stock Incentive Plans - Narrative (Details) - USD ($) | 1 Months Ended | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 31, 2021 | Mar. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2020 | Mar. 25, 2019 | Sep. 25, 2018 | Jun. 21, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Common stock authorized and reserved for future issuance (in shares) |  | 30,928,290 |  | 25,157,139 |  |  |
Stock‑based compensation expense |  | $ 1,780,000 | $ 1,409,000 |  |  |  |
Unrecognized compensation expense related to unvested non-employee stock options |  | $ 0 |  |  |  |  |
Employee stock option grants |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Common stock authorized and reserved for future issuance (in shares) |  | 7,719,817 |  | 4,916,374 |  |  |
Estimated forfeitures rate |  | 10.00% |  |  |  |  |
Weighted average grant date fair value of stock options (in dollars per share) |  | $ 1.99 | $ 1.69 |  |  |  |
Unrecognized compensation expense related to unvested employee stock options |  | $ 11,800,000 |  |  |  |  |
Weighted average period for recognition |  | 2 years 8 months 12 days |  |  |  |  |
Unvested restricted stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Grants in period (in dollars per share) |  | $ 2.99 |  |  |  |  |
Grants in period (in shares) |  | 468,550 |  |  |  |  |
Reserved for issuance (in shares) |  | 98,750 |  |  |  |  |
Reserved for issuance (in dollars per share) |  | $ 2.99 |  |  |  |  |
2016 Plan |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Number of shares authorized for grants (in shares) |  |  |  |  |  |  | 1,210,256
Number of shares authorized, increase (in shares) |  | 4,322,850 | 3,453,022 |  |  |  |
Common stock authorized and reserved for future issuance (in shares) |  | 3,248,520 |  |  |  |  |
2016 Plan | Unvested restricted stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Vested in period |  | $ 1,400,000 |  |  |  |  |
Grants in period (in shares) | 369,800 | 98,750 |  |  |  |  |
Awarded in period (in shares) |  | 197,500 |  |  |  |  |
Reserved for issuance (in shares) |  | 98,750 |  |  |  |  |
Award vesting term |  | 4 years |  |  |  |  |
Employment Inducement Incentive Award Plan |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Number of shares authorized for grants (in shares) |  | 1,358,333 |  |  |  |  |
Common stock authorized and reserved for future issuance (in shares) |  |  |  |  | 2,000,000 | 1,175,000 |
Employment Inducement Incentive Award Plan | Unvested restricted stock units |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Weighted average period for recognition |  | 3 years 1 month 6 days |  |  |  |  |
Unrecognized compensation expense |  | $ 1,500,000 |  |  |  |  |
ESPP |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |
Number of shares authorized, increase (in shares) |  | 1,080,711 | 863,254 |  |  |  |
Common stock authorized and reserved for future issuance (in shares) |  | 2,546,464 |  |  |  |  | 173,076
Stock‑based compensation expense |  | $ 100,000 | $ 100,000 |  |  |  |

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- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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