Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of share-based compensation expense

Share-based compensation expense is as follows (dollars in thousands):

	Years Ended December 31,
	2023		2022		2021
Research and development	$	4,743	$	2,922	$	2,403
Selling, general and administrative	22,016		14,646		15,507
Total	$	26,759	$	17,568	$	17,910

Summary of stock option and SAR activity

The following table summarizes stock option and stock appreciation rights (SAR) activities:

	Number of Options & SARs	Weighted Average Exercise Price (per share)		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2021	5,774,076	$	24.15	5.95	$	41,530
Granted	1,103,635	$	32.12
Exercised	(817,919)	$	12.77
Forfeited	(262,223)	$	30.42
Outstanding, December 31, 2022	5,797,569	$	26.99	6.11	$	53,650
Granted	1,204,643	$	37.78
Exercised	(258,154)	$	16.70
Forfeited	(160,236)	$	33.48
Outstanding, December 31, 2023	6,583,822	$	29.20	5.90	$	23,668
As of December 31, 2023
Vested and expected to vest	6,583,822	$	29.20	5.90	$	23,668
Exercisable	4,110,537	$	26.58	4.43	$	22,305

Schedule of assumptions used in estimation of fair value of each award option on the date of grant using black-scholes option-pricing model

The fair value of each option award is estimated on the date of the grant, using the Black-Scholes option-pricing model and the assumptions in the following table:

	Years Ended December 31,
	2023	2022	2021
Fair value of common stock	$27.66 - $38.60	$28.93 - $35.23	$25.09 - $30.45
Expected volatility	56.87% - 58.22%	58.71% - 60.15%	60.62% - 61.8%
Dividend yield	0%	0%	0%
Expected term	5.60 years - 7.03 years	5.58 years - 6.72 years	5.63 years - 6.56 years
Risk-free interest rate	3.27% - 4.33%	1.87% - 3.70%	0.72% - 1.3%

Restricted stock and restricted stock unit activity

The following table summarizes restricted stock unit (RSU) activities:

	Number of RSUs	Weighted- Average Grant Date Fair Value per Share		Aggregate Intrinsic Value (in thousands)		Aggregate Fair Value (in thousands)
Nonvested, December 31, 2021	21,110	$	29.61
Granted	134,460	$	32.17
Vested	(21,110)	$	29.61	$	69.5	$	625.1
Forfeited	(2,500)	$	32.20
Nonvested, December 31, 2022	131,960	$	32.17
Granted	227,980	$	38.60
Vested	(47,049)	$	32.18	$	1,814.3	$	1,514.0
Forfeited	(12,750)	$	35.68
Nonvested, December 31, 2023	300,141	$	36.90

Performance shares activity

The following table summarizes performance share unit (PSU) activities:

	Performance-Based PSUs			Market-Based Units			Total PSUs
	Number of PSUs	Weighted- Average Grant Date Fair Value per Share		Number of PSUs	Weighted- Average Grant Date Fair Value per Share		Number of PSUs	Weighted- Average Grant Date Fair Value per Share
Nonvested, December 31, 2021	53,500	$	29.82	35,625	$	26.34	89,125	$	28.43
Granted	155,000	$	28.93	—	$	—	155,000	$	28.93
Vested	(22,250)	$	29.69	(15,625)	$	23.41	(37,875)	$	27.10
Forfeited	(4,500)	$	29.94	—	$	—	(4,500)	$	29.94
Nonvested, December 31, 2022	181,750	$	29.07	20,000	$	28.63	201,750	$	29.03
Granted	205,000	$	34.00	—	$	—	205,000	$	34.00
Vested	(132,120)	$	30.72	—	$	—	(132,120)	$	30.72
Forfeited	(3,000)	$	28.93	—	$	—	(3,000)	$	28.93
Nonvested, December 31, 2023	251,630	$	32.22	20,000	$	28.63	271,630	$	31.96