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Stock award plan (Tables) | 12 Months Ended
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Dec. 31, 2017
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, 2014 |  | 3,432,972 |  |  | $ | 25.00 |  |  |  |  |  |
Granted |  | 2,201,800 |  |  | $ | 50.81 |  |  |  |  |  |
Exercised |  | (656,248 | ) |  | $ | 13.27 |  |  |  |  |  |
Forfeited |  | (152,047 | ) |  | $ | 49.58 |  |  |  |  |  |
Outstanding at December 31, 2015 |  | 4,826,477 |  |  | $ | 37.20 |  |  |  |  |  |
Granted |  | 1,500,645 |  |  | $ | 27.90 |  |  |  |  |  |
Exercised |  | (89,216 | ) |  | $ | 10.85 |  |  |  |  |  |
Forfeited |  | (383,590 | ) |  | $ | 47.42 |  |  |  |  |  |
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 |  |  | 7.28 |  | $ | 13,435 |
Vested or expected to vest at December 31, 2017 |  | 2,522,747 |  |  | $ | 23.29 |  |  | 8.39 |  | $ | 6,822 |
Exercisable at December 31, 2017 |  | 3,778,544 |  |  | $ | 33.19 |  |  | 6.48 |  | $ | 6,167 |
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, 2017, 2016 and 2015 were contemporaneously estimated on the date of grant using the following assumptions:
|  | 2017 |  | 2016 |  | 2015
Risk-free interest rate |  | 1.84 - 2.45% |  | 1.30 - 2.24% |  | 1.48 - 2.18%
Expected volatility |  | 76 - 81% |  | 67 - 78% |  | 67 - 69%
Expected term |  | 5.04 - 10.00 years |  | 5.05 - 10.00 years |  | 5.50 - 9.12 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, 2016 |  | 271,651 |  |  | $ | 19.76 |
Granted |  | 365,194 |  |  | $ | 11.67 |
Vested |  | (180,861 | ) |  | $ | 14.19 |
Forfeited |  | (62,973 | ) |  | $ | 14.18 |
Unvested at December 31, 2017 |  | 393,011 |  |  | $ | 15.64 |
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,
|  | 2017 |  | 2016 |  | 2015
Research and development |  | $ | 15,456 |  |  | $ | 16,812 |  |  | $ | 16,138 |
Selling, general and administrative |  | 15,103 |  |  | 18,197 |  |  | 17,841 |
Total |  | $ | 30,559 |  |  | $ | 35,009 |  |  | $ | 33,979 |

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- Definition Tabular disclosure of the changes in outstanding nonvested restricted stock shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -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=27013229&loc=d3e301413-122809 + 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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