Stock Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Option Activity Under Company's Equity Incentive Plans

The following table summarizes stock option activity under the Company’s equity incentive plans and related information:

	Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)
Outstanding — December 31, 2017		821,741		$	13.69		9.17
Options granted		227,900		$	14.83
Options exercised		(59	)	$	4.63
Options canceled/forfeited		(23,189	)	$	4.46
Outstanding — March 31, 2018		1,026,393		$	14.15		9.03
Exercisable — March 31, 2018		228,386		$	34.41		7.72
Vested and expected to vest — March 31, 2018		1,026,393		$	14.15		9.03

Summary of Weighted Average Valuation Assumptions Used to Estimate Fair Value of Employee Stock Options

The fair value of employee stock options was estimated using the following weighted-average assumptions for the three months ended March 31, 2018 and 2017:

	Three Months Ended March 31,
	2018			2017
Employee Stock Options:
Risk-free interest rate		2.40	%		1.57	%
Expected term (in years)		6.01			6.04
Dividend yield		—			—
Volatility		109.32	%		73.28	%
Weighted-average fair value of stock options granted	$	12.34		$	21.15

Summary of Stock-Based Compensation Recognized

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

	Three Months Ended March 31,
	2018		2017
Research and development	$	115	$	20
General and administrative⁽¹⁾		491		100
Total stock-based compensation	$	606	$	120

(1)

2018 includes $0.1 million in modification stock-based compensation expense related to a Board member’s departure.