Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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, 2016		2,168,391			6,127,291			2.60		7.3		7,800
Additional authorized		1,743,247
Granted		(2,986,244	)		2,986,244			5.65
Exercised		—			(420,377	)		1.58
Cancelled		100,411			(100,411	)		3.95
RSUs granted		(56,022	)		—
Balance at December 31, 2017		969,783			8,592,747		$	3.69		7.4	$	47,864
Vested and exercisable at December 31, 2017					5,011,207		$	2.65		6.5	$	33,130
Vested and expected to vest at December 31, 2017					8,303,413		$	3.64		7.4	$	46,655

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

	Year Ended December 31,
	2017		2016		2015
Expected term (in years)		5.9		6.0		5.9
Expected volatility (%)	66.0%		67.1%		68.7%
Risk-free interest rate (%)	2.1%		1.3%		1.8%
Expected dividend yield (%)	0.0%		0.0%		0.0%

Summary of Stock-Based Compensation Expense

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

	Year Ended December 31,
	2017		2016		2015
Research and development	$	952	$	593	$	262
Selling and marketing		303		120		50
General and administrative		4,064		2,194		754
Total stock-based compensation expense	$	5,319	$	2,907	$	1,066