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Stock award plan (Tables) | 12 Months Ended
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Dec. 31, 2019
Share-based Payment Arrangement [Abstract] |
Summary of stock option activity | A summary of stock option activity is as follows:
|  | Number of options |  | Weighted- average exercise price |  | Weighted- average remaining contractual term |  | Aggregate intrinsic value
|  |  |  |  |  |  |  | (in thousands)
Outstanding at December 31, 2016 |  | 5,854,316 |  |  | $ | 34.71 |  |  |  |  |  |
Granted |  | 1,913,873 |  |  | $ | 12.34 |  |  |  |  |  |
Exercised |  | (202,085 | ) |  | $ | 10.80 |  |  |  |  |  |
Forfeited |  | (1,117,462 | ) |  | $ | 33.65 |  |  |  |  |  |
Outstanding at December 31, 2017 |  | 6,448,642 |  |  | $ | 29.00 |  |  |  |  |  |
Granted |  | 3,181,623 |  |  | $ | 26.64 |  |  |  |  |  |
Exercised |  | (633,973 | ) |  | $ | 18.61 |  |  |  |  |  |
Forfeited |  | (461,934 | ) |  | $ | 35.36 |  |  |  |  |  |
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 |  |  | 7.34 years |  | $ | 192,350 |
Vested or expected to vest at December 31, 2019 |  | 5,370,703 |  |  | $ | 31.62 |  |  | 8.83 years |  | $ | 88,165 |
Exercisable at December 31, 2019 |  | 5,242,221 |  |  | $ | 31.37 |  |  | 5.70 years |  | $ | 98,781 |
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, 2019, 2018 and 2017 were contemporaneously estimated on the date of grant using the following assumptions:
|  | 2019 |  | 2018 |  | 2017
Risk-free interest rate |  | 1.58% - 2.63% |  | 2.25% - 3.10% |  | 1.84% - 2.45%
Expected volatility |  | 62% - 92% |  | 64% - 90% |  | 76% - 81%
Expected term |  | 5.75 - 6.11 years |  | 5.03 - 10.00 years |  | 5.04 - 10.00 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
|  | Number of Shares |  | Weighted Average Grant Date Fair Value
Unvested at December 31, 2018 |  | 571,479 |  |  | $ | 17.61 |
Granted |  | 306,549 |  |  | $ | 32.97 |
Vested |  | (181,327 | ) |  | $ | 17.56 |
Forfeited |  | (54,282 | ) |  | $ | 23.14 |
Unvested at December 31, 2019 |  | 642,419 |  |  | $ | 24.50 |
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,
|  | 2019 |  | 2018 |  | 2017
Research and development |  | $ | 20,836 |  |  | $ | 16,096 |  |  | $ | 15,456 |
Selling, general and administrative |  | 21,298 |  |  | 17,156 |  |  | 15,103 |
Total |  | $ | 42,134 |  |  | $ | 33,252 |  |  | $ | 30,559 |

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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=116856206&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=116856206&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=116856206&loc=d3e5070-113901 + Details
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