Equity Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

A summary of stock option activity during the year ended December 31, 2015 is as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)	Total Aggregate Intrinsic Value
Outstanding as of December 31, 2014	3,955,548		$	2.58	7.5	$	—
Granted	1,474,178		1.44		—	—
Exercised	(40,520	)	2.05		—	—
Cancelled	(1,335,601	)	3.27		—	—
Outstanding as of December 31, 2015	4,053,605		$	1.95	8.2	$	—
Vested and expected to vest as of December 31, 2015	3,742,904		$	1.98	8.2	$	—
Exercisable as of December 31, 2015	1,731,331		$	2.29	7.6	$	—

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The following table presents the weighted average assumptions used by the Company to estimate the fair value of stock option grants using the Black-Scholes option-pricing model, as well as the resulting weighted average fair values:



	Year Ended December 31,
	2015			2014			2013
Risk-free interest rate	1.37%-1.87%			1.58% - 1.96%			1.08% - 1.85%
Volatility	66.85%-101.54%			80.75		%	70.00		%
Dividend yield	—		%	—		%	—		%
Expected term	5.25-6.46 years			5.25- 6.608			5.25- 6.25 years
Forfeiture rate	11.54		%	3.60		%	2.66		%
Weighted average fair value	$	1.06		$	1.25		$	1.52

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan

The following table summarizes the total stock-based compensation expense resulting from share-based awards recorded in the Company’s consolidated statements of operations (in thousands):



	Year Ended December 31,
	2015		2014		2013
Research and development	$	199	$	267	$	225
General and administrative	1,011		1,464		1,767
	$	1,210	$	1,731	$	1,992