Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2022

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

Schedule of Activities Under Company's Stock Option Plans

Activities for the Company’s stock option plans for the six months ended June 30, 2022 were as follows:

	Options Outstanding
	Number of  Options			Weighted- Average Exercise Price Per Share
Balances at December 31, 2021		12,192,216		$	9.42
Options granted		3,416,918			3.55
Options exercised		(100,990	)		0.98
Option forfeited/expired		(1,077,318	)		8.93
Balances at June 30, 2022		14,430,826		$	8.13

Total Stock-based Compensation Recognized

Total stock-based compensation recorded related to options, TRSUs, PSUs and the ESPP was as follows:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
	(in thousands)
Stock-based compensation expense:
Research and development	$	2,091	$	1,548	$	3,696	$	2,885
General and administrative		2,399		1,877		4,164		3,574
Total stock-based compensation expense	$	4,490	$	3,425	$	7,860	$	6,459

Time based RSU

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

Schedule of Company's TRSU Activities

Activities for the Company’s TRSUs for the six months ended June 30, 2022 were as follows:

	Number of Shares			Weighted Average Grant Date Fair Value Per Share
Balance at December 31, 2021		433,250		$	5.34
RSU's awarded		655,410			3.89
RSU's vested		—			—
RSU's cancelled		(97,044	)		4.75
Balance at June 30, 2022		991,616		$	4.44

Performance based RSU

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

Schedule of Activities for Company's PSUs

Activities for the Company’s PSUs for the six months ended June 30, 2022 were as follows:

	Number of Shares			Weighted Average Grant Date Fair Value Per Share
Balance at December 31, 2021		435,000		$	5.34
PSU's awarded		—			—
PSU's vested		—			—
PSU's cancelled		(47,500	)		5.34
Balance at June 30, 2022		387,500		$	5.34