Note 5 - Income Taxes - Reconciliation of Income Tax Provision (Details) - USD ($)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income taxes at U.S. statutory rates	$ 7,118,000	$ 10,315,000	$ 16,943,000
State income taxes, net of federal tax benefit	649,000	1,233,000	1,078,000
Restricted stock windfall adjustment	322,000	(176,000)	(1,086,000)
Reduction of deferred tax liability due to rate reduction			(430,000)
Other	(47,000)	9,000	1,000
Total provision for income taxes	$ 8,042,000	$ 11,381,000	$ 16,506,000