Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2023

Share-Based Payment Arrangement [Abstract]

Summary of RSU Activity

The following is a summary of RSU activity under our 2014 EIP and Inducement Plan:

	RSUs
	Shares			Weighted Average Grant Date Fair Value
Balance as of December 31, 2022		6,708,608		$	10.61
Granted		5,278,116		$	3.71
Forfeited		(669,390	)	$	8.63
Vested		(1,554,968	)	$	10.74
Balance as of June 30, 2023		9,762,366		$	6.99

Summary of Stock Option Activity

The following is a summary of stock option activity under our 2014 EIP and Inducement Plan:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Balance as of December 31, 2022		10,645,555		$	16.88		6.4	$	42
Granted		4,693,897			3.64		—		—
Exercised		—			—		—		—
Forfeited or expired		(1,522,660	)		20.95		—		—
Balance as of June 30, 2023		13,816,792		$	11.93		7.6	$	38

Schedule of Common Stock Reserved for Future Issuance Under Equity Incentive Plans

The following shares of common stock were reserved for future issuance under our equity incentive plans as of June 30, 2023:

	Total Shares Reserved
2014 Equity Incentive Plan		22,259,975
2018 Inducement Plan		4,971,721
2014 Employee Stock Purchase Plan		332,735
Total reserved shares of common stock		27,564,431

Schedule of Stock-based Compensation, Related to Employee and Nonemployee Stock Awards

Total stock-based compensation expense related to all employee and non-employee stock awards was as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
	(in thousands)				(in thousands)
Research and development	$	7,195	$	8,993	$	13,965	$	17,499
General and administrative		5,357		5,124		10,351		10,953
Total stock-based compensation expense	$	12,552	$	14,117	$	24,316	$	28,452