Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Option Activity

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

	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at January 1, 2016		4,796,005		$	3.78
Granted		1,781,134		$	1.01
Exercised		(38,749	)	$	0.84
Forfeited		(1,679,712	)	$	5.17
Outstanding at December 31, 2016		4,858,678		$	2.31		7.98	$	—
Vested or expected to vest at December 31, 2016		3,043,129		$	3.04		7.63	$	—
Exercisable at December 31, 2016		2,327,806		$	3.63		7.34	$	—

Assumptions used in Black-Scholes Pricing Model for New Grants

The fair value of stock options subject only to service or performance conditions that are granted to employees is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions noted in the following table:

	Years Ended December 31,
	2016		2015		2014
Volatility factor	72.18% - 74.47%		73.04% - 78.70%		69.38% - 77.92%
Expected term (in years)	3.00 - 6.25		5.50 - 6.25		5.50 - 6.25
Risk-free interest rates	1.07% - 2.01%		1.54% - 1.93%		1.81% - 2.02%
Dividend yield		—		—		—

Restricted Stock Activity

The following table summarizes the restricted stock activity during the year ended December 31, 2016: 

	Number of Shares			Weighted- Average Fair-Value
Unvested at January 1, 2016		42,750		$	1.61
Granted		—			—
Vested/Released		(42,750	)		1.61
Unvested at December 31, 2016		—			—