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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Stock-Based Compensation Expense | The following table shows total stock-based compensation expense recognized in the consolidated statements of operations (in thousands):
|  | Year Ended December 31, |
|  | 2013 |  |  | 2012 |  |  | 2011 |
Research and development |  | $ | 3,204 |  |  | $ | 2,892 |  |  | $ | 3,769 |
General and administrative |  |  | 2,942 |  |  |  | 2,446 |  |  |  | 4,312 |
Total stock-based compensation expense |  | $ | 6,146 |  |  | $ | 5,338 |  |  | $ | 8,081 |
Assumptions Used for Estimating Fair Value of Employee Stock Options | The assumptions used for estimating the fair value of the employee stock options are as follows:
|  | Year Ended December 31, |
|  | 2013 |  |  | 2012 |  |  | 2011 |
Risk-free interest rate |  |  | 1.50-1.88 | % |  |  | 0.74-1.34 | % |  |  | 0.93-2.11 | %
Expected life of option (in years) |  |  | 5.36-5.38 |  |  |  | 5.40-5.58 |  |  |  | 5.39-5.41 |
Expected dividend yield of stock |  |  | 0 | % |  |  | 0 | % |  |  | 0 | %
Expected volatility |  |  | 0.88 |  |  |  | 0.87-0.88 |  |  |  | 0.83-0.86 |
Weighted-Average Assumptions Used for Estimating Fair Value of ESPP Purchase Rights | The weighted-average estimated fair value of shares purchased under the Company’s ESPP during 2013, 2012 and 2011 were $1.47, $2.51 and $1.62, respectively, based upon the assumptions in the Black-Scholes valuation model. The weighted–average assumptions used for estimating the fair value of the ESPP purchase rights are as follows:
|  | Year Ended December 31, |
|  | 2013 |  |  | 2012 |  |  | 2011 |
Risk-free interest rate |  |  | 0.05-0.61 | % |  |  | 0.05-0.30 | % |  |  | 0.05-0.61 | %
Expected life of option (in years) |  |  | 0.5-2.0 |  |  |  | 0.5-2.0 |  |  |  | 0.5-2.0 |
Expected dividend yield of stock |  |  | 0 | % |  |  | 0 | % |  |  | 0 | %
Expected volatility |  |  | 0.51-0.85 |  |  |  | 0.93-1.37 |  |  |  | 0.58-0.85 |

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- Definition Tabular disclosure of the amount of total share-based compensation cost, including the amounts attributable to each share-based compensation plan and any related tax benefits. + 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=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 employee stock purchase plans, including, but not limited to: (a) expected term, (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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- 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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