Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2022

Share-based Payment Arrangement [Abstract]

Summary of Option Activity

A summary of option activity under the Plans for the three months ended March 31, 2022 follows:

(in thousands, except for share and per share amounts)	Number of Shares	Weighted Average Exercise Price at Grant Date		Weighted Average Remaining Term (Years)	Aggregate Intrinsic Value
Outstanding at December 31, 2021	3,721,148	$	14.16	5.77	$	11,327
Granted	646,200	11.36
Outstanding at March 31, 2022	4,367,348	13.75		6.17	3,029
Exercisable at March 31, 2022	2,852,580	13.20		4.65	3,004
Vested and expected to vest at March 31, 2022	4,080,448	13.77		5.94	3,027

Summary of RSU Activity

A summary of RSU activity under the Plans for the three months ended March 31, 2022 follows:

	Number of Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2021	1,764,740	$	17.27
Granted	848,350	11.37
Forfeited	(8,439)	14.68
Vested	(585,857)	17.51
Unvested at March 31, 2022	2,018,794	14.73

Stock-Based Compensation Expense

Stock-based compensation expense recognized for the three months ended March 31, 2022 and 2021 was comprised of the following:

	Three Months Ended
(in thousands)	March 31, 2022		March 31, 2021
Research and development	$	1,160	$	1,120
Selling, general and administrative	3,618		2,789
Total stock-based compensation expense	$	4,778	$	3,909

Black-Scholes-Merton Option Pricing Model for Employee and Director Stock Options Granted

Assumptions used in the Black-Scholes-Merton option pricing model for employee and director stock options granted during the three months ended March 31, 2022 and 2021 were as follows:

	Three Months Ended
	March 31, 2022		March 31, 2021
Expected dividend yield	0	%	0	%
Weighted average expected volatility	47	%	46	%
Weighted average expected term (years)	6.05		5.98
Weighted average risk-free rate	1.86	%	0.73	%