Note 10 - Employee Equity Incentive Plans (Tables)

3 Months Ended

Jun. 30, 2017

Notes Tables

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

	Three Months Ended June 30,
Statement of Operations Classifications	2017		2016
	(unaudited)
Cost of goods sold	$	93	$	100
Research, development and engineering		325		303
Selling, general and administrative		489		452
Stock-based compensation effect in income before income tax provision		907		855
Provision for income tax (1)		363		342
Net stock-based compensation effects in net income	$	544	$	513

Schedule of Employee Service Share Based Compensation Fair Value Assumptions and Methodology [Table Text Block]

	Stock Options						Purchase Plan
	Three Months Ended June 30,						Three Months Ended June 30,
	2017			2016			2017			2016
	(unaudited)						(unaudited)
Weighted average estimated fair value of grant per share	$	6.49		$	3.96		$	2.92		$	3.94
Risk-free interest rate		1.9	%		1.4	%		0.7	%		0.3	%
Expected term in years		6.63			6.41			0.75			1.00
Volatility		36.8	%		41.0	%		29.9	%		42.9	%
Dividend yield (1)		0.0	%		1.4	%		0.0	%		1.4	%

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

				Weighted Average
	Number of			Exercise Price		Intrinsic
	Shares			Per Share		Value (1)
				(unaudited)		(000)
Balance at March 31, 2017		5,097,545		$	10.71
Options granted		549,000		$	16.05
Options exercised		(812,045	)	$	9.40	$	5,187
Options cancelled		(89,750	)	$	11.42
Options expired		(19,000	)	$	9.35
Balance at June 30, 2017		4,725,750		$	11.54
Exercisable at June 30, 2017		2,607,500		$	10.75
Exercisable at March 31, 2017		3,300,295		$	10.34