Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Company's Stock Option Activity and Related Information

A summary of the Company’s stock option activity and related information is as follows:

				Options Outstanding
	Shares Available for Grant			Number of Stock Options Outstanding			Weighted- Average Exercise Price		Weighted- Average Remaining ContractualLife (Years)		Aggregate Intrinsic Value
											(In thousands)
Balance at December 31, 2017		969,783			8,592,747		$	3.69		7.4	$	47,864
Additional options authorized		2,706,158			—
Options granted		(2,003,229	)		2,003,229			7.15
Options exercised		—			(396,939	)		1.80
Options canceled		155,459			(155,459	)		5.41
Balance at June 30, 2018		1,828,171			10,043,578		$	4.43		7.6	$	25,933
Vested and exercisable at June 30, 2018					5,411,367		$	3.08		6.4	$	21,106
Vested and expected to vest at June 30, 2018					9,701,142		$	4.38		7.6	$	25,536

Schedule of Weighted-Average Assumptions Used in Black-Scholes Option-Pricing Model to Estimate Fair Value of Employee Stock Option at Grant Date

The fair value of employee stock option was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:  

	Six Months Ended June 30,
	2018		2017
Expected term (in years)		6.0		6.0
Expected volatility%	61.2%		67.1%
Risk-free interest rate%	2.8%		2.1%
Expected dividend yield%		0.0%		0.0%

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recognized in the Company’s condensed consolidated statements of operations is classified as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development	$	347	$	216	$	550	$	381
Selling and marketing		194		72		321		123
General and administrative		1,142		725		2,002		1,278
Total stock-based compensation expense	$	1,683	$	1,013	$	2,873	$	1,782