Stock Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2020

Summary of Stock Option Activity

	Options Outstanding
		Weighted		Weighted
	Number	Average		Average Remaining	Aggregate
	of	Exercise		Contractual	Intrinsic
	Shares	Price		Term (Years)	Value
Balances at December 31, 2019	16,288	$	3.56
Options granted	210	$	9.00
Options canceled	(287)	$	5.35
Options exercised	(3,460)	$	3.36
Balances at June 30, 2020	12,751	$	3.66	6.98	$	71,487
Options exercisable at June 30, 2020	8,619	$	3.28	6.71	$	51,668

Schedule of Assumptions Used to Estimate Fair Value of Options

Stock Options
	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Dividend yield	—	%	—	%	—	%	—	%
Risk-free interest rate	0.28	%	2.07	%	0.28	%	2.15	%
Expected volatility	69.3	%	56.1	%	69.3	%	56.1	%
Expected term (years)	4.00		4.00		4.00		4.00

Schedule of Stock-Based Compensation Expense by Line Item

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Research and development (1)	$	5,298	$	1,128	$	9,260	$	5,074
Sales and marketing		1,013		55		1,888		881
General and administrative		1,795		852		3,340		2,887
Total stock-based compensation expense (2)	$	8,106	$	2,035	$	14,488	$	8,842

(1) For the three and six months ended June 30, 2020, stock-based compensation expense recorded in research and development includes $486 and $630 from PSUs classified as liabilities.

(2) Stock-based compensation expense for the three and six months ended June 30, 2019 included a reversal of previously accrued expense of $2,526 due to a decrease in the vesting probability of certain performance-based equity awards.

Schedule of compensation expense related to unvested awards

The following table summarizes total compensation expense related to unvested awards not yet recognized as of June 30, 2020:

	Unrecognized Compensation
	Expense for Unvested
	Awards
Stock options	$	8,276
RSUs		33,063
PSUs (1)		7,048
PSOs		638
Total unrecognized compensation expense	$	49,025

(1) The unrecognized compensation expense for PSUs classified as equity and vesting in fiscal years 2022 and 2023, except for PSUs classified as liabilities, is excluded in the table above as the Company does not have a reasonable basis upon which to estimate the vesting probability of such awards in those future periods.

Restricted stock units ("RSUs")

Summary of Company's Performance-based Awards

		Weighted		Weighted
	Number of	Average		Average Remaining		Aggregate
	Units	Grant Date		Contractual		Intrinsic
	Outstanding	Fair Value		Term (Years)		Value
Awarded and unvested, December 31, 2019	3,951	$	5.66
Granted	3,013	$	6.40
Vested	(885)	$	4.88
Forfeited	(190)	$	5.78
Awarded and unvested, June 30, 2020	5,889	$	6.15	1.73	$	54,592

Performance stock units ("PSUs")

Summary of Company's Performance-based Awards

		Weighted		Weighted
	Number of	Average		Average Remaining		Aggregate
	Units	Grant Date		Contractual		Intrinsic
	Outstanding	Fair Value		Term (Years)		Value
Awarded and unvested, December 31, 2019	5,417	$	6.06
Vested	(276)	$	3.61
Forfeited	(1,370)	$	6.85
Awarded and unvested, June 30, 2020	3,771	$	5.95	1.24	$	34,953
PSUs expected to vest at June 30, 2020	1,625	$	5.56	0.63	$	15,068

Performance stock options ("PSOs")

Summary of Stock Option Activity

		Weighted		Weighted
	Number of	Average		Average Remaining		Aggregate
	Shares	Exercise		Contractual		Intrinsic
	Outstanding	Price		Term (Years)		Value
Balance as of December 31, 2019	6,583	$	4.54
Canceled	(1,377)	$	6.18
Exercised	(948)	$	3.61
Balance as of June 30, 2020	4,258	$	4.21	7.53	$	21,531
PSOs expected to vest at June 30, 2020	526	$	3.60	7.35	$	2,984
PSOs exercisable at June 30, 2020	2,800	$	3.59	7.30	$	15,892