Note 6 - Stockholders' Equity (Details Textual) - USD ($)	6 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Oct. 01, 2016
Treasury Stock, Shares, Ending Balance	2,392,928
Treasury Stock, Value, Ending Balance	$ 69,195,000	$ 66,499,000	$ 66,730,000
Common Class A [Member]
Treasury Stock, Shares, Acquired	92,582
Treasury Stock, Value, Acquired, Cost Method	$ 2,689,000
Common Class B [Member]
Treasury Stock, Shares, Acquired	200
Treasury Stock, Value, Acquired, Cost Method	$ 7,000