Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2015

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 and six months ended June 30, 2015 and 2014:

	Three Months Ended June 30,		Six Months Ended June 30,
	2015	2014	2015	2014
Common Stock Options
Risk free interest rate	1.50%	1.66%	1.50%-1.87%	1.66% - 1.77%
Expected option term	5.5 years	5.5 years	5.5-6.0 years	5.5 - 6.0 years
Expected volatility of common stock	76.74%	71.06%	71.99%-76.74%	71.06% - 73.21%
Expected dividend yield	0.0%	0.0%	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 six months ended June 30, 2015 and 2014.

	Three and Six Months Ended June 30,
	2015	2014
Employee Stock Purchase Plan
Risk free interest rate	0.08%	0.08%
Expected option term	6 months	6 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 June 30,		Six Months Ended June 30,
	2015	2014	2015	2014
Research and development	$ 145,509	$ 104,759	$ 288,533	$ 197,424
General and administrative	239,029	160,451	467,605	291,096
Total stock-based compensation expense	$ 384,538	$ 265,210	$ 756,138	$ 488,520