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Stock option plan (Tables) | 12 Months Ended
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Dec. 31, 2020
Stock option plan |
Schedule of assumptions used in valuation of stock options |
|  | Year ended December 31,
|  | 2020 |  | 2019 |  | 2018
Expected volatility |  | 78.9% ‑83.8% |  | 73.5% ‑74.5% |  | 71.5%
Risk‑free rate |  | 0.36% ‑1.43% |  | 1.53% ‑2.63% |  | 2.9%
Expected dividend yield |  | 0% |  | 0% |  | 0%
Expected term in years |  | 5.50-6.08 |  | 6.08-7.59 |  | 8.20
Summary of stock option activity |
|  |  |  |  | Weighted‑ |  | Weighted |  |  |
|  |  |  |  | average |  | average |  |  |
|  |  |  |  | exercise |  | remaining |  | Aggregate
|  | Number of |  | price per |  | contractual |  | intrinsic
|  | options |  | share |  | term (in years) |  | value
Outstanding at January 1, 2018 |  |  | 1,897,206 |  | $ | 1.46 |  | 8.3 |  |  |
Granted |  |  | 24,067 |  |  | 1.01 |  |  |  |  |
Exercised |  |  | (2,306) |  |  | 0.92 |  |  |  |  |
Cancelled/Forfeited |  |  | (74,779) |  |  | 17.31 |  |  |  |  |
Outstanding at December 31, 2018 |  |  | 1,844,188 |  | $ | 0.82 |  | 7.6 |  |  |
Granted |  |  | 2,018,796 |  |  | 8.82 |  |  |  |  |
Exercised |  |  | (322,267) |  |  | 0.23 |  |  |  |  |
Cancelled/Forfeited |  |  | (40,783) |  |  | 0.99 |  |  |  |  |
Outstanding at December 31, 2019 |  |  | 3,499,934 |  | $ | 5.49 |  | 7.5 |  |  |
Granted |  |  | 446,800 |  |  | 35.16 |  |  |  |  |
Exercised |  |  | (164,075) |  |  | 0.92 |  |  |  |  |
Cancelled/Forfeited |  |  | (11,200) |  |  | 38.78 |  |  |  |  |
Outstanding at December 31, 2020 |  |  | 3,771,459 |  | $ | 9.10 |  | 6.8 |  | $ | 6,945,112
Exercisable at December 31, 2020 |  |  | 1,968,116 |  | $ | 3.52 |  | 6.1 |  | $ | 5,602,168
Vested or expected to vest at December 31, 2020 |  |  | 3,771,459 |  | $ | 9.10 |  | 6.8 |  | $ | 6,945,112

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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + 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) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 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 (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + 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 (f)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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