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Stock-based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Schedule of Stock-Based Compensation Expense | The following stock-based compensation amounts were recognized for the periods indicated (in thousands):
|  | Year Ended December 31, |
|  | 2014 |  |  | 2013 |  |  | 2012 |
Research and development |  | $ | 1,562 |  |  | $ | 507 |  |  | $ | 472 |
General and administrative |  |  | 1,682 |  |  |  | 355 |  |  |  | 366 |
Total stock-based compensation expense |  | $ | 3,244 |  |  | $ | 862 |  |  | $ | 838 |
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions | The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions in the following table:
|  | Year Ended December 31,
|  | 2014 |  | 2013 |  | 2012
Expected dividend yield |  | 0% |  | 0% |  | 0%
Expected volatility |  | 67% |  | 53% - 67% |  | 51%
Risk-free interest rate |  | 1.8% - 2.3% |  | 1.2% - 2.2% |  | 1.2%
Expected term. |  | 6.25 years |  | 7 years |  | 7 years
Schedule of Stock Option and Restricted Stock Unit Activity | The following table summarizes stock option and restricted stock unit (RSU) activity for 2014:
|  | Shares |  |  | Weighted- Average Exercise Price |  |  | Weighted-Average Remaining Contractual Term (Years) |  |  | Aggregate Intrinsic Value (in thousands) |
Outstanding, December 31, 2013 |  |  | 3,200,958 |  |  | $ | 4.90 |  |  |  | 6.9 |  |  |  |  |
Granted |  |  | 976,869 |  |  |  | 27.06 |  |  |  |  |  |  |  |  |
Exercised |  |  | (568,906 | ) |  |  | 1.31 |  |  |  |  |  |  |  |  |
Forfeited or expired |  |  | (36,805 | ) |  |  | 9.76 |  |  |  |  |  |  |  |  |
Outstanding, December 31, 2014 |  |  | 3,572,116 |  |  |  | 11.40 |  |  |  | 7.3 |  |  | $ | 84,515 |
December 31, 2014: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercisable |  |  | 1,668,962 |  |  |  | 3.24 |  |  |  | 5.3 |  |  |  | 53,122 |
Vested and expected to vest |  |  | 3,341,192 |  |  |  | 11.03 |  |  |  | 7.2 |  |  |  | 80,323 |

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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 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: 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 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F Reference 4: 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=6415400&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=6415400&loc=d3e5070-113901 + Details
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