Note 12 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

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

	Year Ended December 31,
(in thousands)	2020		2019		2018
Stock options and other	$	13,327	$	9,591	$	10,113
Employee stock purchase plan		1,346		1,190		815
Total stock-based compensation expense	$	14,673	$	10,781	$	10,928
Cost of revenue	$	2,451	$	2,056	$	1,543
Operating expenses:
Marketing and sales		3,121		2,632		1,942
Research and development		2,440		1,851		1,517
General and administrative		6,661		4,242		5,926
Total stock-based compensation expense	$	14,673	$	10,781	$	10,928

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

	Year Ended December 31,
	2020		2019		2018
Risk-free interest rate		0.50 - 1.47%		2.35 - 2.58%		2.52 - 3.07%
Expected life (years)		6.25		6.25		6.25
Expected volatility		42.40 - 43.83%		42.52 - 42.74%		41.68 - 42.22%
Expected dividend yield		0%		0%		0%
Weighted average grant date fair value		$45.32		$47.84		$50.08

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

				Weighted-
				Average
	Stock Options			Exercise Price
Options outstanding at January 1, 2018		399,055		$	51.13
Granted		36,600			110.59
Exercised		(155,765	)		38.92
Cancelled		(27,274	)		74.35
Options outstanding at December 31, 2018		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
Exercisable at December 31, 2020		94,318		$	69.36

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	5,964	1.35	30.58	5,964	30.58
$31.44 to $66.87	78,482	4.81	57.51	56,032	57.18
$66.88 to $96.20	10,591	4.42	74.05	9,343	71.09
$96.21 to $123.10	134,494	8.45	106.81	22,979	108.41

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, 2018		334,831		$	63.29
Granted		106,855			115.41
Restrictions lapsed		(86,191	)		63.64
Forfeited		(31,574	)		68.67
Restricted stock at December 31, 2018		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

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, 2018		25,707		$	58.35
Granted		20,006			105.75
Restrictions lapsed		-			-
Performance change		6,427			58.35
Forfeited		-			-
Performance stock at December 31, 2018		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

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

	Year Ended December 31,
	2020	2019	2018
Risk-free interest rate	0.12 - 0.17%	1.59 - 2.35%	2.06 - 2.33%
Expected life (months)	6.00	6.00	6.00
Expected volatility	50.85 - 59.99%	42.63 - 53.57%	31.50 - 37.36%
Expected dividend yield	0%	0%	0%