Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2016

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 and six months ended June 30, 2016 and 2015:

	Three Months Ended June 30,		Six Months Ended June 30,
	2016	2015	2016	2015
Common Stock Options
Risk free interest rate	1.41%	1.50%	1.25%-1.58%	1.50%-1.87%
Expected option term	5.5 years	5.5 years	5.3-6.0 years	5.5-6.0 years
Expected volatility of common stock	75.03%	76.74%	74.44%-75.91%	71.99%-76.74%
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 three and six months ended June 30, 2016 and 2015.

	Three and Six Months Ended June 30,
	2016		2015
Employee Stock Purchase Plan
Risk free interest rate		0.50%		0.08%
Expected term	6.0 months		6.0 months
Expected volatility of common stock		83.83%		62.91%
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,
	2016		2015		2016		2015
Research and development	$	151,148	$	145,509	$	309,937	$	288,533
General and administrative		275,982		239,029		536,105		467,605
Total stock-based compensation expense	$	427,130	$	384,538	$	846,042	$	756,138