Stock-Based Compensation (Tables)

12 Months Ended

Dec. 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	(1,838)	1,838	$	18.01
Options exercised	—	(2,464)	$	5.29
Options forfeited	340	(340)	$	13.13
Balance at December 31, 2019	6,416	8,497	$	10.39	6.88	$	197,955
Exercisable at December 31, 2019		4,835	$	7.27	5.56	$	127,753
Vested and expected to vest at December 31, 2019		8,288	$	10.29	6.83	$	193,940

Summary of offering activity

	Number of	Total
	Shares Purchased	Proceeds
Offering Period			(in thousands)
November 1, 2017 - April 30, 2018	206,447	$	1,855
May 1, 2018 - October 31, 2018	184,825	$	1,763
November 1, 2018 - April 30, 2019	132,177	$	2,147
May 1, 2019 - October 31, 2019	136,084	$	2,176

Restricted stock units

		Weighted-
		Average
	Number of	Grant Date
	Shares	Fair Value
Balance at December 31, 2018	1,084	$	11.72
Granted	2,019	$	20.97
Vested	(541)	$	12.56
Canceled/Forfeited	(158)	$	16.68
Balance at December 31, 2019	2,404	$	19.86

Summary of stock-based compensation expenses

	Year ended December 31,
	2019						2018						2017
	Employee		Non-Employee		Total		Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	905	$	32	`	937	$	564	$	5	$	569	$	544	$	—	$	544
Research and development		5,354		—		5,354		4,043		—		4,043		3,214		—		3,214
Selling, general and administrative		21,730		603		22,333		9,474		112		9,586		7,644		—		7,644
Total	$	27,989	$	635	$	28,624	$	14,081	$	117	$	14,198	$	11,402	$	—	$	11,402

Performance-based awards

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

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

	December 31,
	2019
Risk-free interest rate		1.63% – 2.61%
Expected dividend yield		—
Expected volatility		50.00%
Expected term (years)		7.25

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

	Year ended December 31,
	2019					2018					2017
Expected term (years)	5.23		—	10.00		5.24		—	5.62		5.14		—	5.24
Expected volatility	42.53	%	—	45.84	%	40.28	%	—	42.53	%	40.75	%	—	62.93	%
Expected dividend rate				0	%				0	%				0	%
Risk-free interest rate	1.60	%	—	2.60	%	2.37	%	—	3.06	%	1.67	%	—	2.16	%

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

	Year ended December 31,
	2018					2017
Expected term (years)	2.72		—	2.76		2.67		—	2.71
Expected volatility	41.36	%	—	43.84	%	41.22	%	—	52.18	%
Expected dividend rate				0	%				0	%
Risk-free interest rate	2.36	%	—	2.86	%	1.42	%	—	1.95	%