Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2015

Equity [Abstract]

Summary of Estimated Fair Value of Stock Option Award

The estimated fair value of each stock option award granted was determined on the date of grant using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for option grants during the three months ended March 31, 2015 and 2014:

	Three Months Ended March 31,
	2015		2014
Stock Options
Risk free interest rate		1.87%		1.77%
Expected option term	6.0 years		6.0 years
Expected volatility of common stock		71.99%		73.21%
Expected dividend yield		0.0%		0.0%

Summary of Estimated Fair Value of Employee Stock Purchase Plan Award

The estimated fair value of each ESPP award was determined on the date of grant using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for option grants during the three months ended March 31, 2015 and 2014.  

	Three Months Ended March 31,
	2015		2014
Employee Stock Purchase Plan
Risk free interest rate		0.08%		0.08%
Expected term	6.0 months		6.0 months
Expected volatility of common stock		62.91%		73.21%
Expected dividend yield		0.0%		0.0%

Summary of Recognized Non-Cash Stock-Based Compensation Expense

The Company recognized non-cash stock-based compensation expense to employees and directors in its research and development and its general and administrative functions as follows:

	Three Months Ended March 31,
	2015		2014
Research and development	$	143,024	$	92,665
General and administrative		228,576		130,645
Total stock-based compensation expense	$	371,600	$	223,310