Stockholders' Equity (Tables)

9 Months Ended

Sep. 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 nine months ended September 30, 2015 and 2014 (no stock options were granted during the three months ended September 30, 2015 and 2014):

	Nine Months Ended
	September 30,
	2015		2014
Common Stock Options
Risk free interest rate	1.50% - 1.87%		1.66% - 1.77%
Expected option term	5.5 - 6.0 years		5.5 - 6.0 years
Expected volatility of common stock	71.99% - 76.74%		71.06% - 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 and nine months ended September 30, 2015 and 2014.

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2015		2014		2015		2014
Employee Stock Purchase Plan
Risk free interest rate		0.26%		0.05%	0.08% - 0.26%		0.05 - 0.08%
Expected option term	6 months		6 months		6 months		6 months
Expected volatility of common stock		69.64%		69.32%	62.91% - 69.64%		69.32 - 73.21%
Expected dividend yield		0.0%		0.0%		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				Nine Months Ended
	September 30,				September 30,
	2015		2014		2015		2014
Research and development	$	144,719	$	105,145	$	433,252	$	302,569
General and administrative		226,956		198,816		694,561		489,912
Total stock-based compensation expense	$	371,675	$	303,961	$	1,127,813	$	792,481