Note 10 - Employee Equity Incentive Plans - Stock-based Compensation in Income Tax Provision (Details) - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Stock-based Compensation Effect in Income before Taxes		$ 3,438	$ 3,592	$ 2,867
Provision for income tax		694	660	1,009
Net stock-based compensation effects on net income		2,744	2,932	1,858
Cost of Sales [Member]
Stock-based Compensation Effect in Income before Taxes		362	488	433
Research and Development Expense [Member]
Stock-based Compensation Effect in Income before Taxes	[1]	1,144	1,272	814
Selling, General and Administrative Expenses [Member]
Stock-based Compensation Effect in Income before Taxes		$ 1,932	$ 1,832	$ 1,620

[1] Includes acquisition-related compensation expenses of $249,000 during fiscal 2016.