Note 12 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Notes Tables

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]

	Year Ended December 31,
(in thousands)	2015			2014			2013
Stock options and other	$	5,580		$	4,386		$	3,084
Employee stock purchase plan		502			423			377
Total stock-based compensation expense	$	6,082		$	4,809		$	3,461
Cost of revenue	$	513		$	386		$	316
Operating expenses:
Marketing and sales		1,074			927			610
Research and development		1,285			1,048			754
General and administrative		3,210			2,448			1,781
Total stock-based compensation expense	$	6,082		$	4,809		$	3,461
Income tax benefits		(1,859	)		(1,524	)		(847	)
Total stock-based compensation expense, net of tax	$	4,223		$	3,285		$	2,614

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

	Year Ended December 31,
	2015				2014				2013
Risk-free interest rate		1.69	-	1.77%		0.43	-	2.14%		1.03	-	1.98%
Expected life (years)		5.50	-	6.50		2.00	-	6.50		5.50	-	6.50
Expected volatility		46.80	-	47.23%		47.29	-	49.30%		49.36	-	53.54%
Expected dividend yield			0%				0%				0%
Weighted average grant date fair value		$	32.42			$	32.65			$	25.86

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

				Weighted-
				Average
	Stock Options			Exercise Price
Options outstanding at January 1, 2013		1,691,357		$	11.11
Granted		187,615			49.69
Exercised		(695,777	)		7.79
Cancelled		(39,945	)		23.48
Options outstanding at December 31, 2013		1,143,250			19.03
Granted		116,050			72.17
Exercised		(253,544	)		13.77
Cancelled		(6,769	)		26.23
Options outstanding at December 31, 2014		998,987			26.49
Granted		110,335			67.36
Exercised		(316,761	)		14.36
Cancelled		(26,519	)		51.72
Options outstanding at December 31, 2015		766,042		$	36.52
Exercisable at December 31, 2015		409,301		$	19.28

Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by 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 ($)		Number Exercisable		Weighted Average Exercise Price ($)
$	0.00	to	$	7.85		59,441		2.76	$	5.03		59,441	$	5.03
	$	7.86				206,955		4.98		7.86		206,955		7.86
$	7.87	to	$	31.43		138,831		6.15		28.19		72,495		27.22
$	31.44	to	$	47.15		88,146		7.10		45.14		19,504		42.70
$	47.16	to	$	66.87		96,474		7.87		57.52		36,934		55.87
$	66.88	to	$	78.59		176,195		8.75		71.54		13,972		78.53

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

				Weighted-
				Average
				Grant Date
	Restricted			Fair Value
	Stock Awards			Per Share
Restricted stock at January 1, 2014		-		$	-
Granted		77,647			69.18
Restrictions lapsed		(798	)		62.68
Forfeited		(275	)		62.68
Restricted stock at December 31, 2014		76,574			69.27
Granted		68,580			68.89
Restrictions lapsed		(16,863	)		69.25
Forfeited		(3,898	)		72.14
Restricted stock at December 31, 2015		124,393		$	68.97

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

	Year ended December 31,
	2015			2014			2013
Risk-free interest rate	0.08	-	0.39%	0.01	-	0.11%	0.11	-	0.13%
Expected life (months)		6.00			6.00			6.00
Expected volatility	29.41	-	37.64%	37.64	-	39.80%	39.80	-	53.32%
Expected dividend yield		0%			0%			0%