Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 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	(1,837)	1,837	$	18.00
Options exercised	—	(2,138)	$	4.87
Options forfeited/cancelled	364	(364)	$	13.93
Balance at September 30, 2019	6,441	8,798	$	10.27	7.10	$	198,252
Exercisable at September 30, 2019		4,811	$	7.09	5.74	$	123,680
Vested and expected to vest at September 30, 2019		8,603	$	10.18	7.06	$	194,605

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	1,765	$	18.72
Vested	(419)	$	11.86
Canceled/forfeited	(161)	$	16.68
Balance at September 30, 2019	2,269	$	17.69

Summary of stock-based compensation expenses

	Three months ended  September 30,
	2019						2018
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	258	$	11	$	269	$	176	$	15	$	191
Research and development		1,580		—		1,580		1,047		—		1,047
Selling, general and administrative		8,312		86		8,398		2,292		86		2,378
Total	$	10,150	$	97	$	10,247	$	3,515	$	101	$	3,616

	Nine months ended September 30,
	2019						2018
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	641	$	21	$	662	$	466	$	20	$	486
Research and development		3,738		—		3,738		2,963		—		2,963
Selling, general and administrative		15,184		518		15,702		6,606		83		6,689
Total	$	19,563	$	539	$	20,102	$	10,035	$	103	$	10,138

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  September 30,										Nine months ended September 30,
	2019					2018					2019					2018
Expected term (years)	5.23		—	10.00		5.35		—	5.50		5.23		—	10.00		5.24		—	5.62
Expected volatility	43.07	%	—	45.84	%	40.59	%	—	41.05	%	42.53	%	—	45.84	%	40.28	%	—	41.05	%
Expected dividend rate				0.00	%				0.00	%				0.00	%				0.00	%
Risk-free interest rate	1.60	%	—	2.12	%	2.75	%	—	2.97	%	1.60	%	—	2.60	%	2.37	%	—	2.97	%

Non-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			Nine months ended
	September 30, 2018			September 30, 2018
Expected term (years)		2.76		2.72		—	2.76
Expected volatility		41.36	%	41.36	%	—	42.03	%
Expected dividend rate		0.00	%				0.00	%
Risk-free interest rate		2.86	%	2.36	%	—	2.86	%