Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2020

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

Schedule of performance-based awards

Period Granted	Options Granted	RSUs Granted	Options Vested	RSUs Vested	Milestone	Valuation Method
(in thousands)
Q1 2019	200	300	119	184	(1)	Monte-Carlo Simulation
Q2 2019	—	188	—	—	(2)	Fair Market Value
Q3 2019	—	50	—	25	(1)	Monte-Carlo Simulation
Q1 2020	150	300	—	—	(1)	Monte-Carlo Simulation
Q1 2020	—	436	—	—	(3)	Fair Market Value
Q1 2020	129	—	—	—	(3)	Black-Scholes-Merton
Q2 2020	—	21	—	—	(3)	Fair Market Value

________________________________

(1) The awards will vest based on the achievement of certain values of the Company’s common stock at multiple thresholds within certain periods and are contingent upon the completion of requisite service through the date of such vesting.

(2) The vesting of the awards will be triggered after the end of the achievement milestone, as measured by the Company.

(3) The awards will vest based on achievement of certain revenue target and are contingent upon the completion of requisite service through the date of such vesting.

Summary of stock option activity

	Outstanding Options
					Weighted-
			Weighted-		Average
	Shares		Average		Remaining	Aggregate
	Available for	Number of	Exercise		Contractual	Intrinsic
	Grant	Shares	Price		Life	Value
(in thousands, except for contractual life and exercise price)					(In years)
Balance at December 31, 2019	6,416	8,497	$	10.39	6.88	$	197,955
Additional shares authorized	3,120	—
Options granted	(446)	446	$	26.75
Options exercised	—	(1,037)	$	10.42
Options forfeited/cancelled	84	(84)	$	16.00
RSUs granted	(4,670)	—
RSUs forfeited/cancelled	210	—
Balance at June 30, 2020	4,714	7,822	$	11.26	6.55	$	301,915
Exercisable at June 30, 2020		5,523	$	5.77	8.84	$	226,552
Vested and expected to vest at June 30, 2020		7,682	$	11.16	6.52	$	297,314

Restricted stock units

		Weighted-
		Average
		Grant Date
	Shares	Fair Value
(in thousands, except for grant date fair value)
Balance at December 31, 2019	2,404	$	19.86
Granted	2,335	$	27.89
Vested	(578)	$	15.50
Cancelled/forfeited	(105)	$	21.58
Balance at June 30, 2020	4,056	$	24.10

Summary of stock-based compensation expenses

	Three months ended June 30,
	2020						2019
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	441	$	—	$	441	$	215	$	10	$	225
Research and development		2,631		282		2,913		1,264		—		1,264
Selling, general and administrative		8,527		76		8,603		4,226		89		4,315
Total	$	11,599	$	358	$	11,957	$	5,705	$	99	$	5,804

	Six months ended June 30,
	2020						2019
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	755	$	—	$	755	$	383	$	10	$	393
Research and development		4,313		442		4,755		2,157		—		2,157
Selling, general and administrative		13,779		85		13,864		6,873		432		7,305
Total	$	18,847	$	527	$	19,374	$	9,413	$	442	$	9,855

Performance-based awards

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

Schedule of assumptions used in valuation of fair value

	June 30,
	2020
Risk-free interest rate		0.61	%	—	1.64	%
Expected dividend yield					0.00	%
Expected volatility		55	%	—	65	%
Expected term (years)		5.25		—	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

	Three months ended June 30,								Six months ended June 30,
	2020			2019					2020					2019
Expected term (years)		10.0		5.30		—	10.00		5.27		—	10.00		5.30		—	10.00
Expected volatility		53.94	%	42.71	%	—	43.49	%	49.94	%	—	58.53	%	42.53	%	—	43.49	%
Expected dividend rate		0.00	%				0.00	%				0.00	%				0.00	%
Risk-free interest rate		0.71	%	1.78	%	—	2.51	%	0.44	%	—	1.70	%	1.78	%	—	2.60	%