Note 9 - Employee Equity Incentive Plans - Stock-based Compensation in Income Tax Provision (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based Compensation Effect in Income before Taxes		$ 1,098	$ 874	$ 2,005	$ 1,729
Provision for income tax	[1]	439	350	802	692
Net stock-based compensation effects in net income		659	524	1,203	1,037
Cost of Sales [Member]
Stock-based Compensation Effect in Income before Taxes		107	96	200	196
Research and Development Expense [Member]
Stock-based Compensation Effect in Income before Taxes		416	283	741	586
Selling, General and Administrative Expenses [Member]
Stock-based Compensation Effect in Income before Taxes		$ 575	$ 495	$ 1,064	$ 947

[1] Calculated at the U.S. statutory income tax rate of 40% in fiscal 2018 and 2017.