Note 12 - Equity Incentive Plan (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

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

	2017			2016			2015
Risk free interest rate	1.60%	-	1.86%	0.94%	-	1.55%	1.15%	-	1.46%
Expected volatility	38.74%	-	44.31%	47.33%	-	51.61%	53.15%	-	54.65%
Expected life (years)		4.0			4.5			4.5
Expected dividend yield		0.00%			0.00%			0.00%

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	2017		2016		2015
Cost of product revenue	$	439	$	148	$	42
Research & development		564		467		269
Selling, general & administrative		4,804		2,777		1,914
Total stock-based compensation expense	$	5,807	$	3,392	$	2,225

Schedule of Share-based Compensation, Stock Options and Stock Appreciation Rights Award Activity [Table Text Block]

	2017					2016
				Weighted					Weighted
				Average					Average
				Exercise					Exercise
	Number of			Price Per		Number of			Price Per
	Shares			Share		Shares			Share
Options and SAR's outstanding at beginning of year		979,569		$	26.15		762,260		$	18.75
Granted		440,688		$	50.22		354,275		$	40.77
Cancelled		(74,527	)	$	45.56		(58,841	)	$	30.05
Expired		(589	)	$	32.86		(3,310	)	$	11.37
Exercised		(17,941	)	$	20.56		(74,815	)	$	15.46
Options and SAR's outstanding at end of year		1,327,200		$	33.70		979,569		$	26.15

Schedule of Share-based Compensation, Exercisable Stock Options and Stock Appreciation Rights Award Activity [Table Text Bloc]

	Outstanding		Weighted Average Exercise Price		Weighted Average Remaining Term (in years)
Incentive stock options		182,472	$	14.12		4.3
Nonqualified stock options		374,211	$	20.18		5.3
Performance options		32,598	$	38.79		7.7
SAR's		35,250	$	6.36		2.1

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]

	2017					2016
				Weighted					Weighted
				Average					Average
	Number of			Grant Date		Number of			Grant Date
	Shares			Fair Value		Shares			Fair Value
Unvested at Beginning of year		207,077		$	36.44		150,384		$	34.29
Granted		67,567		$	52.03		87,158		$	38.11
Cancelled		-		$	-		(4,950	)	$	36.20
Expired		-		$	-		-		$	-
Vested/Released		(45,418	)	$	35.32		(25,515	)	$	33.35
Unvested at end of year		229,226		$	42.47		207,077		$	36.44