Equity Incentive Plan (Tables)

9 Months Ended

Sep. 30, 2022

Equity [Abstract]

Summary of Stock Option Activity

The following table summarizes the stock option activity for the nine months ended September 30, 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		3,857		$	3.26
Exercised		—		$	—
Expired and forfeited		(2,301	)	$	19.10
Outstanding at September 30, 2022		20,500		$	15.76		6.31

Summary of Restricted Stock Unit Activity

The following table summarizes the restricted stock unit activity (“RSUs”) for the nine months ended September 30, 2022:

	Shares (in thousands)			Weighted-Average Grant Date Fair Value
Outstanding at December 31, 2021		2,803		$	11.51
Granted		1,159		$	2.73
Released		(667	)	$	11.58
Expired and forfeited		(478	)	$	11.49
Outstanding at September 30, 2022		2,817		$	7.88

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 September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
Research and development	$	4,921	$	4,521	$	13,906	$	14,130
General and administrative		2,932		2,836		8,717		8,414
Sales and marketing		3,345		3,879		9,843		11,419
Total stock-based compensation expense	$	11,198	$	11,236	$	32,466	$	33,963

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:

	For the Nine Months Ended
	September 30,
	2022			2021
Risk-free interest rate		3.1	%		1.0	%
Dividend yield		0.0	%		0.0	%
Volatility		61.1	%		65.8	%
Expected life (years)		6			6