Note 13 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Notes Tables

Share-based Payment Arrangement, Cost by Plan [Table Text Block]

	Year Ended December 31,
(in thousands)	2021		2020		2019
Stock options and other	$	17,553	$	13,327	$	9,591
Employee stock purchase plan		1,542		1,346		1,190
Total stock-based compensation expense	$	19,095	$	14,673	$	10,781
Cost of revenue	$	2,595	$	2,451	$	2,056
Operating expenses:
Marketing and sales		3,736		3,121		2,632
Research and development		2,833		2,440		1,851
General and administrative		9,931		6,661		4,242
Total stock-based compensation expense	$	19,095	$	14,673	$	10,781

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year Ended December 31,
	2021		2020		2019
Risk-free interest rate		0.80 - 1.12%		0.50 - 1.47%		2.35 - 2.58%
Expected life (years)		6.25		6.25		6.25
Expected volatility		45.28 - 45.53%		42.40 - 43.83%		42.52 - 42.74%
Expected dividend yield		0%		0%		0%
Weighted average grant date fair value		$128.14		$45.32		$47.84

Share-based Payment Arrangement, Option, Activity [Table Text Block]

				Weighted-
				Average
	Stock Options			Exercise Price
Options outstanding at January 1, 2019		252,616		$	64.71
Granted		53,708			105.81
Exercised		(16,079	)		48.67
Cancelled		(13,979	)		89.50
Options outstanding at December 31, 2019		276,266			72.38
Granted		60,065			105.79
Exercised		(68,958	)		57.00
Cancelled		(37,842	)		67.92
Options outstanding at December 31, 2020		229,531			86.46
Granted		57,901			128.14
Exercised		(28,991	)		58.78
Cancelled		(25,057	)		109.31
Options outstanding at December 31, 2021		233,384		$	97.78
Exercisable at December 31, 2021		115,700		$	81.30

Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block]

	Options Outstanding, Vested and Expected to Vest			Options Exercisable
Range of Exercise Prices	Number Outstanding	Weighted Average Remaining Contractual Life	Weighted Average Exercise Price ($)	Number Exercisable	Weighted Average Exercise Price ($)
$7.76 to $31.43	4,624	0.35	30.58	4,624	30.58
$31.44 to $66.87	50,159	3.58	57.13	45,986	57.02
$66.88 to $96.20	41,586	7.82	89.95	9,570	71.68
$96.21 to $180.46	137,015	7.67	117.31	55,520	107.28

Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block]

				Weighted-
				Average
				Grant Date
	Restricted			Fair Value
	Stock Awards			Per Share
Restricted stock at January 1, 2019		323,921		$	79.85
Granted		115,471			106.35
Restrictions lapsed		(92,597	)		77.25
Forfeited		(31,822	)		87.58
Restricted stock at December 31, 2019		314,973			89.55
Granted		108,179			111.76
Restrictions lapsed		(101,941	)		84.70
Forfeited		(14,012	)		94.24
Restricted stock at December 31, 2020		307,199			98.87
Granted		205,996			123.61
Restrictions lapsed		(115,908	)		91.26
Forfeited		(53,505	)		128.05
Restricted stock at December 31, 2021		343,782		$	111.79

Schedule of Nonvested Performance-based Units Activity [Table Text Block]

				Weighted-
				Average
				Grant Date
	Performance			Fair Value
	Stock Awards			Per Share
Performance stock at January 1, 2019		52,140		$	76.54
Granted		21,434			104.99
Restrictions lapsed		-			-
Performance change		(61,816	)		88.06
Forfeited		(2,375	)		105.37
Performance stock at December 31, 2019		9,383			58.35
Granted		19,956			118.66
Restrictions lapsed		(7,113	)		58.35
Performance change		-			-
Forfeited		(2,270	)		58.35
Performance stock at December 31, 2020		19,956			118.66
Granted		15,078			203.64
Restrictions lapsed		-			-
Performance change		(10,366	)		192.95
Forfeited		(7,829	)		113.91
Performance stock at December 31, 2021		16,839		$	115.56

Schedule of Share-based Payment Award, Awards Other Than Stock Options, Valuation Assumptions [Table Text Block]

	Year Ended December 31,
	2021	2020	2019
Risk-free interest rate	0.06 - 0.17%	0.12 - 0.17%	1.59 - 2.35%
Expected life (months)	6.00	6.00	6.00
Expected volatility	53.44 - 65.53%	50.85 - 59.99%	42.63 - 53.57%
Expected dividend yield	0%	0%	0%