Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

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 Contractual Life (Years)		Aggregate Intrinsic Value
											(In thousands)
Balance at December 31, 2018		1,908,626			11,603,708		$	6.64		7.6	$	10,151
Additional options authorized		3,853,280
Options granted		(2,493,505	)		2,493,505			8.35
Options exercised		-			(1,701,627	)		4.82
Options canceled		410,410			(410,410	)		6.67
RSUs granted		(679,325	)
RSUs canceled		48,413
Balance at June 30, 2019		3,047,899			11,985,176		$	7.20		8.2	$	21,838
Vested and exercisable at June 30, 2019					3,467,682		$	4.50		6.5	$	14,977
Vested and expected to vest at June 30, 2019					11,351,730		$	7.16		8.1	$	21,454

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

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

	Six Months Ended June 30,
	2019		2018
Expected term (in years)		6.0		6.0
Expected volatility%	60.1%		61.2%
Risk-free interest rate%	2.5%		2.8%
Expected dividend yield%		0.0%		0.0%

Summary of RSU Activity (Detail)

	RSUs
	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2018		1,736,234		$	9.65
RSUs granted		679,325			7.75
RSUs vested		(36,981	)		6.26
Unvested at June 30, 2019		2,378,578		$	9.22
Vested and unreleased		104,019
Outstanding at June 30, 2019		2,482,597

Summary of Stock-Based Compensation Expense

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	453	$	347	$	844	$	550
Selling and marketing		347		194		612		321
General and administrative		4,107		1,142		8,003		2,002
Total stock-based compensation expense	$	4,907	$	1,683	$	9,459	$	2,873