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Stock-based Compensation | 3 Months Ended
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Mar. 31, 2014
Stock-based Compensation [Abstract] |
Stock-based Compensation | 7. Stock-based Compensation In the first quarter of 2014, the Board of Directors of the Company approved grants under the Company’s Long Term Incentive Plan for an aggregate of 1,099,239 stock options and an aggregate of 972,614 RSUs to certain employees of the Company. The stock options vest monthly over four years, and the RSUs vest annually over three years, in equal increments. The Company recognizes compensation expense for all stock-based payment awards made to the Company’s employees, consultants and directors based on estimated fair values. The valuation of stock option awards is determined at the date of grant using the Black-Scholes Model. This model requires inputs such as the expected term of the option, expected volatility and risk-free interest rate. To establish an estimate of expected term, the Company considers the vesting period and contractual period of the award and its historical experience of stock option exercises, post-vesting cancellations and volatility. The estimate of expected volatility is based on the Company’s historical volatility. The risk-free rate is based on the yield available on U.S. Treasury zero-coupon issues. The forfeiture rate impacts the amount of aggregate compensation for both stock options and RSUs. To establish an estimate of forfeiture rate, the Company considers its historical experience of option forfeitures and terminations. The fair value of the stock options granted was estimated based on the following weighted average assumptions for three months ended March 31, 2014 and 2013:
|  | Three Months Ended March 31, |
|  | 2014 |  |  | 2013 |
Dividend yield |  |  | 0 | % |  |  | 0 | %
Expected volatility |  |  | 94 | % |  |  | 92 | %
Risk-free interest rate |  |  | 1.73 | % |  |  | 0.78 | %
Expected term |  | 5.6 years |  |  | 5.6 years |
Stock option activity for the three months ended March 31, 2014 was as follows:
|  | Options |  |  | Weighted Average Exercise Price Per Share |  |  | Weighted Average Remaining Contractual Life (in years) |  |  | Aggregate Intrinsic Value (in thousands) |
Options outstanding at December 31, 2013 |  |  | 7,218,241 |  |  | $ | 8.42 |  |  |  | 6.75 |  |  | $ | 18,213 |
Granted |  |  | 1,099,239 |  |  |  | 8.56 |  |  |  |  |  |  |  |  |
Exercised |  |  | (640,649 | ) |  |  | 4.72 |  |  |  |  |  |  |  |  |
Forfeited, expired or cancelled |  |  | (116,766 | ) |  |  | 24.72 |  |  |  |  |  |  |  |  |
Options outstanding at March 31, 2014 |  |  | 7,560,065 |  |  | $ | 8.50 |  |  |  | 7.14 |  |  | $ | 9,892 |
Options exercisable at March 31, 2014 |  |  | 4,562,868 |  |  | $ | 10.85 |  |  |  | 5.95 |  |  | $ | 5,422 |
The valuation of RSUs is determined at the date of grant using the closing stock price. To establish an estimate of forfeiture rate, the Company considers its historical experience of forfeitures and terminations. Unvested RSU activity for the three months ended March 31, 2014 is summarized below:
|  |  |  |  | Weighted- |
|  | Number of |  |  | Average Grant- |
|  | Shares |  |  | Date Fair Value |
Unvested balance at December 31, 2013 |  |  | 1,738,037 |  |  | $ | 2.73 |
Granted |  |  | 972,614 |  |  |  | 8.64 |
Vested |  |  | (478,845 | ) |  |  | 4.16 |
Forfeited |  |  | (77,536 | ) |  |  | 2.82 |
Unvested balance at March 31, 2014 |  |  | 2,154,270 |  |  | $ | 5.08 |
The following table shows total stock-based compensation expense included in the condensed consolidated statements of comprehensive loss for the three months ended March 31, 2014 and 2013 (in thousands):
|  | Three Months Ended March 31, |
|  | 2014 |  |  | 2013 |
Research and development |  | $ | 2,406 |  |  | $ | 997 |
Selling, general and administrative |  |  | 1,518 |  |  |  | 622 |
Total stock-based compensation expense |  | $ | 3,924 |  |  | $ | 1,619 |

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- Definition The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -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 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 50 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6406099&loc=d3e25284-112666 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5444-113901 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 + Details
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