Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Summary of stock option activity

	Outstanding Options
					Weighted-
			Weighted-		Average
	Shares		Average		Remaining	Aggregate
	Available for	Number of	Exercise		Contractual	Intrinsic
(in thousands, except for contractual life and exercise price)	Grant	Shares	Price		Life	Value
					(In years)
Balance at December 31, 2018	5,431	9,463	$	7.69	6.91	$	61,718
Additional shares authorized	2,483	—
Options granted	(1,195)	1,195	$	16.57
Options exercised	—	(1,070)	$	2.41
Options forfeited/cancelled	55	(55)	$	11.24
Balance at March 31, 2019	6,774	9,533	$	9.37	7.39	$	107,874
Exercisable at March 31, 2019		5,016	$	6.36	6.02	$	71,540
Vested and expected to vest at March 31, 2019		9,312	$	9.29	7.35	$	106,097

Restricted stock units

		Weighted-
		Average
		Grant Date
(in thousands, except for grant date fair value)	Shares	Fair Value
Balance at December 31, 2018	1,084	$	11.72
Granted	1,202	$	18.35
Vested	(187)	$	9.46
Canceled/forfeited	(14)	$	11.70
Balance at March 31, 2019	2,085	$	15.74

Summary of stock-based compensation expenses

	Three months ended  March 31,
	2019						2018
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	168	$	—	$	168	$	138	$	4	$	142
Research and development		894		—		894		903		—		903
Selling, general and administrative		2,646		343		2,989		2,108		1		2,109
Total	$	3,708	$	343	$	4,051	$	3,149	$	5	$	3,154

Employee stock options

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of assumptions used in valuation of fair value of employee stock options

	Three months ended  March 31,
	2019					2018
Expected term (years)	5.33		—	5.53		5.24		—	5.59
Expected volatility	42.53	%	—	42.75	%	40.28	%	—	40.88	%
Expected dividend rate				0.00	%				0.00	%
Risk-free interest rate	2.26	%	—	2.60	%	2.37	%	—	2.70	%