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Stock award plan - (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2021
Share-based Payment Arrangement [Abstract] |
Summary of stock option activity | A summary of stock option activity is as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted- |  |  | ​ | ​
​ | ​ | ​ | ​ | Weighted- | ​ | average | ​ | ​ | Aggregate
​ | ​ | ​ | ​ | average | ​ | remaining | ​ | ​ | intrinsic
​ | ​ | Number of | ​ | exercise | ​ | contractual | ​ | ​ | value(in
​ | ​ | options | ​ | price | ​ | term | ​ | ​ | thousands)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ |  | ​ | ​ | ​
Outstanding at December 31, 2018 |  | 8,534,358 | ​ | $ | 28.58 |  |  |  | ​ | ​ |
Granted |  | 3,977,995 | ​ | $ | 35.81 |  |  |  | ​ | ​ |
Exercised |  | (949,887) | ​ | $ | 19.25 |  |  |  | ​ | ​ |
Forfeited |  | (518,527) | ​ | $ | 35.27 |  |  |  | ​ | ​ |
Outstanding at December 31, 2019 |  | 11,043,939 | ​ | $ | 31.67 |  |  |  | ​ | ​ |
Granted |  | 2,777,975 | ​ | $ | 51.06 |  |  |  | ​ | ​ |
Exercised |  | (3,268,452) | ​ | $ | 24.25 |  |  |  | ​ | ​ |
Forfeited |  | (889,785) | ​ | $ | 42.14 |  |  |  | ​ | ​ |
Outstanding at December 31, 2020 |  | 9,663,677 | ​ | $ | 38.72 |  |  |  | ​ | ​ |
Granted |  | 2,487,234 | ​ | ​ | 61.36 |  |  |  | ​ | ​ |
Exercised |  | (635,871) | ​ | ​ | 28.01 |  |  |  | ​ | ​ |
Forfeited/Cancelled |  | (742,458) | ​ | ​ | 52.04 |  |  |  | ​ | ​ |
Outstanding at December 31, 2021 |  | 10,772,582 | ​ | $ | 43.66 |  | 6.91 | years | ​ | $ | 50,564
Vested or Expected to vest at December 31, 2021 |  | 4,409,301 | ​ | $ | 51.05 |  | 8.34 | years | ​ | $ | 7,022
Exercisable at December 31, 2021 |  | 5,958,347 | ​ | $ | 37.53 |  | 5.74 | years | ​ | $ | 43,249
​
Schedule of assumptions used to estimate fair values of grants made on the date of grant | The fair values of grants made in the years ended December 31, 2021, 2020 and 2019 were contemporaneously estimated on the date of grant using the following assumptions: ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​
​ | 2021 |  | 2020 |  | 2019
Risk-free interest rate | 0.51% - 1.24% |  | 0.34% - 1.45% |  | 1.58% - 2.63%
Expected volatility | 74% - 89% |  | 87% - 89% |  | 62% - 92%
Expected term | 5.5 years |  | 5.75 years |  | 5.75 - 6.11 years
​
Summary of information on the Company's restricted stock | The following table summarizes information on the Company’s restricted stock awards and units: ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Restricted Stock Awards and Units
​ | ​ | ​ | ​ | Weighted
​ | ​ | ​ | ​ | Average
​ | ​ | ​ | ​ | Grant
​ | ​ | Number of | ​ | Date
​ |  | Shares |  | Fair Value
Unvested at December 31, 2020 | ​ | 982,058 | ​ | $ | 41.78
Granted |  | 1,018,228 | ​ | ​ | 62.54
Vested |  | (335,114) | ​ | ​ | 36.09
Forfeited |  | (145,341) | ​ | ​ | 57.71
Unvested at December 31, 2021 |  | 1,519,831 | ​ | $ | 55.43
​
Schedule of share-based compensation expense recorded in the statement of operations | The Company recorded share-based compensation expense in the statement of operations related to incentive stock options, nonstatutory stock options, restricted stock awards, restricted stock units and the ESPP as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year ended December 31,
​ | ​ | 2021 |  | 2020 |  | 2019
Research and development | ​ | $ | 53,632 | ​ | $ | 38,716 | ​ | $ | 20,836
Selling, general and administrative | ​ |  | 49,881 | ​ |  | 31,609 | ​ |  | 21,298
Total | ​ | $ | 103,513 | ​ | $ | 70,325 | ​ | $ | 42,134
​

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- Definition Tabular disclosure of the changes in outstanding nonvested restricted stock shares. + 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) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. + 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 (h)(1) -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 S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=122041274&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 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901 + Details
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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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