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Stock award plan - (Tables) | 6 Months Ended
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Jun. 30, 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, 2018 |  | 8,534,358 |  |  | $ | 28.58 |  |  |  |  |  |
Granted |  | 2,845,620 |  |  | $ | 33.54 |  |  |  |  |  |
Exercised |  | (311,002 | ) |  | $ | 16.50 |  |  |  |  |  |
Forfeited/Cancelled |  | (215,675 | ) |  | $ | 36.10 |  |  |  |  |  |
Outstanding at June 30, 2019 |  | 10,853,301 |  |  | $ | 30.07 |  |  | 7.59 years |  | $ | 178,906 |
Vested or Expected to vest at June 30, 2019 |  | 5,334,168 |  |  | $ | 29.22 |  |  | 9.01 years |  | $ | 84,446 |
Exercisable at June 30, 2019 |  | 5,138,717 |  |  | $ | 30.90 |  |  | 5.98 years |  | $ | 88,423 |
Schedule of assumptions used to estimate fair values of grants made on the date of grant | The fair value of grants made in the six months ended June 30, 2019 was contemporaneously estimated on the date of grant using the following assumptions:
|  | Six months ended June 30, 2019
Risk-free interest rate |  | 1.98 - 2.63%
Expected volatility |  | 61.90 - 63.09%
Expected term |  | 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
|  | Number of Shares |  | Weighted Average Grant Date Fair Value
January 1, 2019 |  | 571,479 |  |  | $ | 17.61 |
Granted |  | 304,549 |  |  | $ | 32.94 |
Vested |  | (179,577 | ) |  | $ | 17.54 |
Forfeited |  | (31,449 | ) |  | $ | 21.47 |
Unvested at June 30, 2019 |  | 665,002 |  |  | $ | 24.45 |
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:
|  | Three Months Ended June 30, |  | Six Months Ended June 30,
|  | 2019 |  | 2018 |  | 2019 |  | 2018
Research and development |  | $ | 5,516 |  |  | $ | 3,932 |  |  | $ | 10,203 |  |  | $ | 7,678 |
Selling, general and administrative |  | 5,404 |  |  | 4,152 |  |  | 9,981 |  |  | 8,153 |
Total |  | $ | 10,920 |  |  | $ | 8,084 |  |  | $ | 20,184 |  |  | $ | 15,831 |

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