Note 15 - Share-based Compensation

6 Months Ended

Jun. 30, 2025

Notes to Financial Statements

Share-Based Payment Arrangement [Text Block]

Note 15.  Share-Based Compensation

Equity Plans

The Company’s board of directors and stockholders approved the following equity plans:

● the 2013 Equity Incentive Plan ("2013 Plan")

● the 2021 Equity Incentive Plan ("2021 Plan")

● the 2023 Equity Inducement Plan ("Inducement Plan")

The Company has issued stock options, restricted stock awards ("RSAs") and restricted stock units ("RSUs") to employees, consultants and non-employee directors. Stock option awards generally vest over a four-year period and have a maximum term of ten years. Stock options under these plans have been granted with an exercise price equal to the fair market value on the date of the grant. Nonqualified and Incentive Stock Options, RSAs and RSUs may be granted from these plans.

Performance Based Incentive Plan

​Starting in 2021, certain senior executives were granted performance stock units ("PSUs") under our Amended and Restated 2021 Equity Incentive Plan ("2021 Plan"), which generally vest over a three-year period subject to achievement of certain pre-established performance metrics. The number of shares of common stock that would ultimately be issued to settle PSUs granted ranged from 0% to 200% of the target number of shares granted. We estimate the fair value of the PSUs on the date of grant using a Monte Carlo simulation model, with stock-based compensation expense recognized ratably over the applicable three-year performance period. The Company recognized stock-based compensation expense for the PSUs for the three months ended  June 30, 2025 and 2024 of $1.2 million and $3.8 million, respectively. The Company recognized stock-based compensation expense for the PSUs for the six months ended  June 30, 2025 and 2024 of $2.1 million and $4.8 million, respectively. 

The following is a summary of PSU activity for the six months ended June 30, 2025:

		​		Weighted					​
				Average		Weighted		Aggregate
	Number of			Exercise		Average		Intrinsic
	shares			Price		Fair Value		Value
	(in thousands, except price data and Contractual Life)
Outstanding at January 1, 2025		1,447			—	$	7.72	$	53,347
Granted		719			—		6.94		8,851
Exercised		(978	)	$	14.76		2.48		14,431
Forfeited		—			—		—		—
Outstanding, June 30, 2025		1,189			—		11.55		30,541
Vested and expected to vest		1,189			—	$	11.55	$	30,541

As of June 30, 2025, there was $7.4 million of unrecognized stock-based compensation expense related to outstanding PSUs, which expense is expected to be recognized over 2.0 years.

Restricted Stock Units

The following is a summary of RSU activity:

				Weighted
				Average Share		Weighted		Aggregate
	Number of			Price on Date		Average Fair		Intrinsic
	shares			of Release		Value		Value
	(in thousands, except price data)
Outstanding, January 1, 2025		2,231			—	$	6.04	$	82,243
Granted		481			—		12.23		5,887
Released		(636	)	$	20.33		6.26		12,940
Cancelled/Forfeited		(21	)		—		6.82		542
Outstanding, June 30, 2025		2,055			—		7.42		52,797
Vested and expected to vest		2,055			—	$	7.42	$	52,797

As of June 30, 2025, there was $13.8 million of unrecognized compensation expense related to these RSUs. This expense is expected to be recognized over 2.5 years.

Share-Based Compensation

Employee share-based compensation expenses recognized for the periods indicated (in thousands):

	Three months ended				Six months ended
	June 30,				June 30,
	2025		2024		2025		2024
Share-based compensation - by expense types
Cost of goods sold	$	94	$	137	$	177	$	239
Research and development		331		478		607		757
Sales and marketing		499		541		822		826
General and administrative		2,240		4,902		4,120		7,075
Total share-based compensation expense	$	3,164	$	6,058	$	5,726	$	8,897