Note 13 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

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

	Year Ended December 31,
(in thousands)	2019		2018		2017
Stock options and other	$	9,591	$	10,113	$	7,954
Employee stock purchase plan		1,190		815		604
Total stock-based compensation expense	$	10,781	$	10,928	$	8,558
Cost of revenue	$	2,056	$	1,543	$	970
Operating expenses:
Marketing and sales		2,632		1,942		1,429
Research and development		1,851		1,517		1,091
General and administrative		4,242		5,926		5,068
Total stock-based compensation expense	$	10,781	$	10,928	$	8,558

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

	Year Ended December 31,
	2019		2018		2017
Risk-free interest rate		2.35 - 2.58%		2.52 - 3.07%		2.24 - 2.36%
Expected life (years)		6.25		6.25		6.5
Expected volatility		42.52 - 42.74%		41.68 - 42.22%		42.68 - 44.68%
Expected dividend yield		0%		0%		0%
Weighted average grant date fair value		$47.84		$50.08		$32.26

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

				Weighted-
				Average
	Stock Options			Exercise Price
Options outstanding at January 1, 2017		569,639		$	45.00
Granted		60,100			69.06
Exercised		(187,313	)		35.93
Cancelled		(43,371	)		61.02
Options outstanding at December 31, 2017		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
Exercisable at December 31, 2019		152,423		$	59.26

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	23,883	1.98		25.04	23,883		25.04
31.44 to 66.87	125,022	4.42		58.67	85,656		58.81
66.88 to 96.20	45,255	4.49		70.98	33,445		70.41
96.21 to 123.10	82,106	8.68		107.79	9,439		110.36

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, 2017		215,105		$	62.78
Granted		210,744			63.70
Restrictions lapsed		(60,102	)		63.60
Forfeited		(30,916	)		61.99
Restricted stock at December 31, 2017		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

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, 2017		-		$	-
Granted		25,707			58.35
Restrictions lapsed		-			-
Forfeited		-			-
Performance stock at December 31, 2017		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

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

	Year Ended December 31,
	2019	2018	2017
Risk-free interest rate	1.59 - 2.35%	2.06 - 2.33%	0.97 - 1.48%
Expected life (months)	6.00	6.00	6.00
Expected volatility	42.63 - 53.57%	31.50 - 37.36%	24.49 - 34.51%
Expected dividend yield	0%	0%	0%