Equity Incentive Plan (Tables)

3 Months Ended

Mar. 31, 2022

Equity [Abstract]

Summary of Stock Option Activity

The following table summarizes the stock option activity for the three months ended March 31, 2022:

	Shares (in thousands)			Weighted- average Exercise Price		Weighted- average Remaining Contractual Term (Years)
Outstanding at December 31, 2021		18,944		$	18.71		6.59
Granted		74		$	6.09
Exercised		—		$	—
Expired and forfeited		(313	)	$	20.06
Outstanding at March 31, 2022		18,705		$	18.64		6.16

Summary of Restricted Stock Unit Activity

The following table summarizes the restricted stock unit activity (“RSUs”) for the three months ended March 31, 2022:

	Shares (in thousands)			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2021		2,803		$	11.51
Granted		17		$	5.97
Released		(214	)	$	11.40
Expired and forfeited		(76	)	$	11.55
Outstanding at March 31, 2022		2,530		$	11.48

Summary of Stock-Based Compensation Expense related to Stock-Based Payment Awards Granted

The following table summarizes stock-based compensation expense related to stock-based payment awards granted pursuant to all of our equity compensation arrangements (in thousands):

	Three Months Ended March 31,
	2022		2021
Research and development	$	4,563	$	4,937
General and administrative		3,002		2,786
Sales and marketing		3,350		3,763
Total stock-based compensation expense	$	10,915	$	11,486

Summary of Fair Value of Option Grant on Grant Date Using Black-Scholes Option Pricing Model

We estimated the fair value of each option grant on the grant date using the Black-Scholes option pricing model with the following weighted-average assumptions:

	March 31,
	2022			2021
Risk-free interest rate		2.1	%		0.7	%
Dividend yield		0.0	%		0.0	%
Volatility		59.1	%		69.4	%
Expected life (years)		6			6