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Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2014

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,
		2014				2013				2012
Research and development		$	5,064			$	3,204			$	2,892
General and administrative			4,136				2,942				2,446
Total stock-based compensation expense		$	9,200			$	6,146			$	5,338

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,
		2014				2013				2012
Risk-free interest rate		1.60-1.70%				1.50-1.88%				0.74-1.34%
Expected life of option (in years)		5.28-5.33				5.36-5.38				5.40-5.58
Expected dividend yield of stock			0	%			0	%			0	%
Expected volatility		0.66-0.69					0.88			0.87-0.88

Weighted-Average Assumptions Used for Estimating Fair Value of ESPP Purchase Rights

The weighted–average assumptions used for estimating the fair value of the ESPP purchase rights are as follows:

		Year Ended December 31,
		2014				2013				2012
Risk-free interest rate		0.05-0.30%				0.05-0.61%				0.05-0.30%
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		0.52-0.75				0.51-0.85				0.93-1.37

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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)

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-Section S99

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-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809



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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

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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.

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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

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-Paragraph 2

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