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Stock award plan (Tables) | 3 Months Ended
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Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [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 |  | 2,490,970 |  |  | $ | 33.01 |  |  |  |  |  |
Exercised |  | (80,826 | ) |  | $ | 15.85 |  |  |  |  |  |
Forfeited/Cancelled |  | (133,119 | ) |  | $ | 29.10 |  |  |  |  |  |
Outstanding at March 31, 2019 |  | 10,811,383 |  |  | $ | 29.67 |  |  | 7.72 years |  | $ | 117,201 |
Vested or Expected to vest at March 31, 2019 |  | 5,364,300 |  |  | $ | 28.40 |  |  | 9.15 years |  | $ | 53,343 |
Exercisable at March 31, 2019 |  | 4,987,460 |  |  | $ | 31.00 |  |  | 6.04 years |  | $ | 60,063 |
Schedule of assumptions used to estimate fair values of grants made on the date of grant | The fair value of grants made in the three months ended March 31, 2019 was contemporaneously estimated on the date of grant using the following assumptions:
|  | Three months ended March 31, 2019
Risk-free interest rate |  | 2.53 - 2.63%
Expected volatility |  | 62.62 - 63.01%
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 |  | (161,077 | ) |  | $ | 17.60 |
Forfeited |  | (19,612 | ) |  | $ | 20.42 |
Unvested at March 31, 2019 |  | 695,339 |  |  | $ | 24.27 |
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 March 31,
|  | 2019 |  | 2018
Research and development |  | $ | 4,686 |  |  | $ | 3,747 |
Selling, general and administrative |  | 4,577 |  |  | 4,001 |
Total |  | $ | 9,263 |  |  | $ | 7,748 |

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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=109197908&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the allocation of equity-based compensation costs to a given line item on the balance sheet and income statement for the period. This may include the reporting line for the costs and the amount capitalized and expensed. + 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=109197908&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=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 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109197908&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=109197908&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=109197908&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=109197908&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=109197908&loc=d3e5070-113901 + Details
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