Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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	(1,697)	1,697	$	17.94
Options exercised	—	(1,468)	$	4.08
Options forfeited/cancelled	286	(286)	$	14.10
Balance at June 30, 2019	6,503	9,406	$	9.90	7.24	$	166,273
Exercisable at June 30, 2019		5,028	$	6.51	5.79	$	105,948
Vested and expected to vest at June 30, 2019		9,219	$	9.80	7.19	$	163,939

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	1,625	$	17.70
Vested	(273)	$	10.24
Canceled/forfeited	(105)	$	15.86
Balance at June 30, 2019	2,331	$

Summary of stock-based compensation expenses

	Three months ended  June 30,
	2019						2018
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	215	$	10	$	225	$	152	$	1	$	153
Research and development		1,264		—		1,264		1,013		—		1,013
Selling, general and administrative		4,226		89		4,315		2,206		(4)		2,202
Total	$	5,705	$	99	$	5,804	$	3,371	$	(3)	$	3,368

	Six months ended June 30,
	2019						2018
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	383	$	10	$	393	$	290	$	5	$	295
Research and development		2,157		—		2,157		1,916		—		1,916
Selling, general and administrative		6,873		432		7,305		4,314		(3)		4,311
Total	$	9,413	$	442	$	9,855	$	6,520	$	2	$	6,522

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  June 30,										Six months ended June 30,
	2019					2018					2019					2018
Expected term (years)	5.30		—	10.00		5.61		—	5.62		5.30		—	10.00		5.24		—	5.62
Expected volatility	42.71	%	—	43.49	%	40.77	%	—	40.98	%	42.53	%	—	43.49	%	40.28	%	—	40.98	%
Expected dividend rate				0.00	%				0.00	%				0.00	%				0.00	%
Risk-free interest rate	1.78	%	—	2.51	%	2.70	%	—	2.86	%	1.78	%	—	2.60	%	2.37	%	—	2.86	%

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			Six months ended
	June 30, 2018			June 30, 2018
Expected term (years)		2.75		2.72		—	2.75
Expected volatility		42.03	%	41.48	%	—	42.03	%
Expected dividend rate		0.00	%				0.00	%
Risk-free interest rate		2.58	%	2.36	%	—	2.58	%