Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Calculation of Fair Value Assumptions Using Black Scholes Option Model

The estimated fair values of employee stock options granted during the year ended December 31, 2016 and 2015, were determined on the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	For the year ended December 31,
	2016	2015
Expected option life (years)	6.22	6.22
Risk-free interest rate	1.26% – 2.12%	1.79% – 2.12%
Expected volatility	70.0% – 76.0%	76.0% – 132.0%
Expected dividend yield	0%	0%

Summary of Stock Option Activity

The following table summarizes stock option activity for the year ended December 31, 2016:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding — January 1, 2016		2,316,569		$	8.59		8.46	$	1,403
Granted		764,850		$	2.79
Exercised		(277	)	$	1.71
Forfeited or expired		(251,841	)	$	10.04
Outstanding — December 31, 2016		2,829,301		$	6.89		7.85	$	—
Exercisable — December 31, 2016		1,299,157		$	6.82		6.73	$	—
Vested and expected to vest — December 31, 2016		2,770,405		$	6.84		7.83	$	—

Summary of Restricted Stock Unit Activity

The following table summarizes RSU activity for the year ended December 31, 2016:

	Number of Units			Weighted- Average Grant Date Fair Value		Total Grant Date Fair Value
Outstanding — January 1, 2016		109,682		$	11.97	$	1,314
Granted		—
Vested		(104,495	)		12.30		(1,285	)
Forfeited or expired		—			—		—
Outstanding — December 31, 2016		5,187		$	5.50	$	29

Stock-Based Compensation Expense

The following table presents total stock-based compensation expense for the years ended December 31, 2016 and 2015, respectively:

	For the years ended December 31,
	2016		2015
Research and development	$	763	$	404
General and administrative		3,235		5,104
Total stock based compensation expense	$	3,998	$	5,508

Hercules Warrants [Member]

Calculation of Fair Value Assumptions Using Black Scholes Option Model

The fair value of the warrants was determined using the Black-Scholes option pricing model, using the following assumptions:

Exercise price	$	8.35
Fair value of underlying stock	$	11.80
Expected volatility		72.52	%
Contractual term		5 years
Risk-free interest rate		1.68	%
Expected dividend yield		0	%

MTS Warrants [Member]

Calculation of Fair Value Assumptions Using Black Scholes Option Model

The fair value of the warrant was determined using the Black-Scholes option pricing model, using the following assumptions:

Exercise price	$	11.80
Fair value of underlying stock	$	11.80
Expected volatility		72.0	%
Contractual term		5 years
Risk-free interest rate		1.54	%
Expected dividend yield		0	%