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Stock award plan (Tables) | 9 Months Ended
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Sep. 30, 2018
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, 2017 |  | 6,448,642 |  |  | $ | 29.00 |  |  |  |  |  |
Granted |  | 2,914,139 |  |  | $ | 25.84 |  |  |  |  |  |
Exercised |  | 512,145 |  |  | $ | 17.03 |  |  |  |  |  |
Forfeited/Cancelled |  | (329,404 | ) |  | $ | 34.20 |  |  |  |  |  |
Outstanding at September 30, 2018 |  | 9,545,522 |  |  | $ | 28.44 |  |  | 7.45 years |  | $ | 172,859 |
Vested or Expected to vest at September 30, 2018 |  | 3,914,413 |  |  | $ | 24.38 |  |  | 8.93 years |  | $ | 89,547 |
Exercisable at September 30, 2018 |  | 4,316,071 |  |  | $ | 32.33 |  |  | 5.99 years |  | $ | 77,003 |
Schedule of assumptions used to estimate fair values of grants made on the date of grant | The fair value of grants made in the nine months ended September 30, 2018 was contemporaneously estimated on the date of grant using the following assumptions:
|  | Nine months ended September 30, 2018
Risk-free interest rate |  | 2.25%—3.03%
Expected volatility |  | 64%—90%
Expected term |  | 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
January 1, 2018 |  | 393,011 |  |  | $ | 15.64 |
Granted |  | 354,691 |  |  | $ | 19.09 |
Vested |  | (113,795 | ) |  | $ | 16.36 |
Forfeited |  | (53,560 | ) |  | $ | 17.24 |
Unvested at September 30, 2018 |  | 580,347 |  |  | $ | 17.60 |
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 September 30, |  | Nine Months Ended September 30,
|  | 2018 |  | 2017 |  | 2018 |  | 2017
Research and development |  | $ | 4,431 |  |  | $ | 3,624 |  |  | $ | 12,109 |  |  | $ | 11,986 |
Selling, general and administrative |  | 4,511 |  |  | 3,544 |  |  | 12,664 |  |  | 12,096 |
Total |  | $ | 8,942 |  |  | $ | 7,168 |  |  | $ | 24,773 |  |  | $ | 24,082 |

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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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