Note 10 - Employee Equity Incentive Plans (Tables)

6 Months Ended

Sep. 30, 2015

Notes Tables

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

	Three Months Ended September 30,				Six Months Ended S eptember 30,
Statement of Operations Classifications	2015		2014		2015		2014
	(unaudited)				(unaudited)
Cost of goods sold	$	124	$	102	$	246	$	210
Research, development and engineering expenses (1)		330		189		791		378
Selling, general and administrative expenses		497		406		903		790
Stock-based compensation effect in income before taxes		951		697		1,940		1,378
Provision for income taxes (2)		333		244		679		482
Net stock-based compensation effects in net income	$	618	$	453	$	1,261	$	896

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

	Stock Options												Purchase Plan (1)
	Three Months Ended September 30,						Six Months Ended September 30,						Six Months Ended September 30,
	2015			2014			2015			2014			2015			2014
	(unaudited)						(unaudited)						(unaudited)
Weighted average estimated fair value of grant per share	$	4.31		$	5.54		$	4.83		$	5.54		$	3.15		$	2.90
Risk-free interest rate		1.7	%		1.8	%		1.8	%		1.8	%		0.1	%		0.1	%
Expected term in years		6.35			6.25			6.45			6.25			1.00			0.50
Volatility		42.8	%		52.2	%		44.9	%		52.2	%		33.7	%		34.5	%
Dividend yield		1.3	%		1.0	%		1.2	%		1.0	%		1.1	%		1.1	%

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

	Number of Shares			Weighted Average Exercise Price Per Share		Intrinsic  Value (1)
				(unaudited)			(000)
Balance at March 31, 2015		4,942,511		$	10.37
Options granted		1,124,000		$	11.72
Options exercised		(320,826	)	$	9.15	$	1,291
Options cancelled		(2,500	)	$	12.13
Options expired		(434,788	)	$	14.68
Balance at September 30, 2015		5,308,397		$	10.38
Exercisable at September 30, 2015		3,504,063		$	9.84
Exercisable at March 31, 2015		3,942,261		$	10.20