Equity Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2019

Schedule of Stock Option Plan Activity

Stock Options

The following table summarizes stock option activity for the three months ended March 31, 2019:

	Options Outstanding
	Shares Available for Grant			Number of Shares Underlying Options			Weighted- Average Exercise Price		Aggregate Intrinsic Value
									(Inthousands)
Balance—December 31, 2018		7,255,050			8,986,010		$	7.54	$	5,458
Authorized		3,182,868			—
RSUs canceled		212,466			—
Granted		(3,861,900	)		3,861,900			3.93
Exercised		—			(254,481	)		0.99
Canceled		802,723			(802,723	)		10.33
Balance—March 31, 2019		7,591,207			11,790,706		$	6.31	$	9,675
Options exercisable—March 31, 2019					5,676,204		$	7.19	$	9,295
Options vested and expected to vest—March 31, 2019					11,685,590		$	6.30	$	9,671

Summary of Restricted Stock Unit or RSU Activity

The following table summarizes RSU activity for the three months ended March 31, 2019:

	RSUs Outstanding
	Number of RestrictedStock Units			Weighted- Average Grant Date FairValue Per Share
Balance—December 31, 2018		1,600,218		$	8.81
Granted		—			—
Vested		(25,850	)		11.15
Canceled/forfeited		(212,466	)		8.43
Balance—March 31, 2019		1,361,902		$	8.83

Summary of Stock-Based Compensation

Total stock-based compensation expense recognized was as follows (in thousands):

	Three Months Ended March 31,
	2019		2018
Research and development	$	2,033	$	2,745
General and administrative		1,670		2,179
Total stock-based compensation expense	$	3,703	$	4,924

Employees

Schedule of Black-Scholes Option-Pricing Model

The fair value of stock option awards granted to employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended March 31,
	2019	2018
Expected term (in years)	5.88 - 6.06	6.02 - 6.04
Volatility	70.7 - 70.9%	71.6 - 71.7%
Risk-free interest rate	2.47 - 2.60%	2.38 - 2.68%
Dividend yield	—%	—%

Non Employees

Schedule of Black-Scholes Option-Pricing Model

The fair value of stock option awards granted to nonemployees was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended March 31,
	2019	2018
Expected term (in years)	6.01 - 9.49	6.42 - 9.84
Volatility	70.7 - 70.8%	71.6 - 71.7%
Risk-free interest rate	2.50 - 2.61%	2.60 - 2.84%
Dividend yield	—%	—%

2015 ESPP

Schedule of Black-Scholes Option-Pricing Model

The following table summarizes the assumptions used in the Black-Scholes option-pricing model to determine fair value of the Company’s common shares to be issued under the 2015 ESPP:

	Three Months Ended March 31,
	2019	2018
Expected term (in years)	0.5	0.5
Volatility	62.5%	49.3%
Risk-free interest rate	2.37%	1.39%
Dividend yield	—%	—%