Note 13 - Equity Incentive Plan (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

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

	2018			2017			2016
Risk free interest rate	2.15%	-	2.82%	1.60%	-	1.86%	0.94%	-	1.55%
Expected volatility	37.12%	-	45.61%	38.74%	-	44.31%	47.33%	-	51.61%
Expected life (years)	4.0	-	4.5		4.0			4.5
Expected dividend yield		0.00%			0.00%			0.00%

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]

	Twelve Months Ended December 31,
	2018		2017
Grants:
Stock options		199,970		440,688
RSAs		64,578		26,306
RSUs		15,457		9,970
Exercises:
Stock options		284,548		12,941
SARs		-		5,000

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

	2018			2017		2016
Cost of product revenue	$	(160	)	$	439	$	148
Research & development		851			564		467
Selling, general & administrative		10,355			4,804		2,777
Total stock-based compensation expense	$	11,046		$	5,807	$	3,392

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

	2018
	Number of Shares			Weighted Average Exercise Price Per Share
Options and SARs outstanding at beginning of year		1,327,200		$	33.70
Granted		199,970		$	58.11
Cancelled		(104,629	)	$	50.19
Expired		(1,079	)	$	46.49
Exercised		(284,548	)	$	10.14
Options and SARs outstanding at end of year		1,136,914		$	42.06

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

	Number  Outstanding		Weighted Avg Exercise Price		Weighted Average Remaining Term (in years)
Incentive stock options		139,674	$	24.53		4.1
Non-qualified stock options		453,790	$	40.74		3.2
Performance awards		100,963	$	40.72		3.1
Stock appreciation rights		35,250	$	6.36		1.1

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

	2018
	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at Beginning of year		229,226		$	42.47
Granted		80,035		$	58.84
Cancelled		(126,946	)	$	42.47
Vested/Released		(123,232	)	$	50.80
Unvested at end of year		59,083		$	47.26