Note 10 - Employee Equity Incentive Plans - Stock-based Compensation in Income Tax Provision (Details) - USD ($) $ in Thousands		3 Months Ended
		Jun. 30, 2017	Jun. 30, 2016
Stock-based Compensation Effect in Income before Taxes		$ 907	$ 855
Provision for income tax	[1]	363	342
Net stock-based compensation effects in net income		544	513
Cost of Sales [Member]
Stock-based Compensation Effect in Income before Taxes		93	100
Research and Development Expense [Member]
Stock-based Compensation Effect in Income before Taxes		325	303
Selling, General and Administrative Expenses [Member]
Stock-based Compensation Effect in Income before Taxes		$ 489	$ 452

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