Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Activity Under Stock Incentive Plans

A summary of activity under the stock incentive plans is as follows (in thousands, except share data and price per share):

	Shares Subject to Outstanding Options			Weighted- Average Exercise Price Per Share		Aggregate Intrinsic Value
Outstanding — Balance at December 31, 2016		4,578,782		$	4.38	$	—
Options granted		2,180,217			0.68
Options exercised		—		N/A
Options cancelled and forfeited		(893,233	)		3.42
Outstanding — Balance at September 30, 2017		5,865,766		$	3.15	$	—
Vested and expected to vest — September 30, 2017		5,804,209		$	3.16	$	—
Exercisable —September 30, 2017		2,787,853		$	3.91	$	—

Weighted-Average Fair Value Assumption of Stock Option Awards

The fair value of stock option awards to executives, employees, and other service providers was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumption:

	Three Months Ended September 30,			Nine Months Ended September 30,
		2017	2016		2017	2016
Expected term (years)		6.00	6.11		6.12	6.06
Expected volatility		80%	88%		79%	90%
Risk-free interest rate		1.94%	1.32%		1.89%	1.73%
Dividend yield		—	—		—	—