Note 11 - Employee Equity Incentive Plans (Tables)

6 Months Ended

Sep. 30, 2016

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 September 30,
Statement of Operations Classifications	2016		2015		2016		2015
	(unaudited)				(unaudited)
Cost of goods sold	$	96	$	124	$	196	$	246
Research, development and engineering (1)		283		330		586		791
Selling, general and administrative		495		497		947		903
Stock-based compensation effect in income before income tax provision		874		951		1,729		1,940
Provision for income tax (2)		350		333		692		679
Net stock-based compensation effects in net income	$	524	$	618	$	1,037	$	1,261

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,
	2016			2015			2016			2015			2016			2015
	(unaudited)						(unaudited)						(unaudited)
Weighted average estimated fair value of grant per share	$	4.99		$	4.31		$	4.40		$	4.83		$	3.94		$	3.15
Risk-free interest rate		1.3	%		1.7	%		1.3	%		1.8	%		0.3	%		0.1	%
Expected term in years		6.41			6.35			6.41			6.45			1.00			1.00
Volatility		42.0	%		42.8	%		41.4	%		44.9	%		42.9	%		33.7	%
Dividend yield (2)		-			1.3	%		0.8	%		1.2	%		1.4	%		1.1	%

Schedule of 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, 2016		5,234,397		$	10.40
Options granted		387,000		$	11.23
Options exercised		(105,997	)	$	7.95	$	375
Options cancelled		(7,500	)	$	13.37
Options expired		(5,000	)	$	9.73
Balance at September 30, 2016		5,502,900		$	10.50
Exercisable at September 30, 2016		3,950,650		$	10.12
Exercisable at March 31, 2016		3,619,563		$	9.93