Note B - Change in Accounting Principle - Change in Accounting Principle From LIFO to Average Cost (Details) - USD ($)	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018	Apr. 01, 2017
Costs of goods sold	$ 41,395,596	$ 26,308,987	$ 132,883,924	$ 72,426,245
Income tax provision	216,094	559,967	2,023,422	889,855
Net earnings	$ 664,773	$ 161,271	$ 6,265,582	$ 920,935
Basic (in dollars per share)	$ 0.09	$ 0.02	$ 0.89	$ 0.13
Diluted (in dollars per share)	$ 0.09	$ 0.02	$ 0.89	$ 0.13
Change in inventories			$ (14,085,601)	$ (11,939,413)
Change in deferred income taxes				810,705
Change in income taxes payable			175,845	32,698
Inventories	$ 59,415,035		59,415,035		$ 45,329,434
Deferred income tax liability	1,798,048		1,798,048		1,872,166
Retained earnings	41,925,545		41,925,545		36,711,380
Earnings before income taxes	880,867	$ 721,238	8,289,004	1,810,790
Change in Inventory Costing Method from LIFO to Average Cost [Member]
Retained earnings						$ 4,418,318
Computed under LIFO [Member]
Income tax provision	545,478		1,412,796
Net earnings	$ 1,687,567		$ 4,369,614
Basic (in dollars per share)	$ 0.24		$ 0.62
Diluted (in dollars per share)	$ 0.24		$ 0.62
Earnings before income taxes	$ 2,233,044		$ 5,782,409
Previously Reported [Member]
Costs of goods sold		26,364,387		72,884,773
Income tax provision		542,909		748,674
Net earnings		$ 122,929		$ 603,588
Basic (in dollars per share)		$ 0.02		$ 0.09
Diluted (in dollars per share)		$ 0.02		$ 0.09
Change in inventories				$ (11,480,885)
Change in deferred income taxes				702,222
Change in income taxes payable
Inventories					38,039,332
Deferred income tax liability					103,198
Retained earnings					31,190,246
Restatement Adjustment [Member] | Change in Inventory Costing Method from LIFO to Average Cost [Member]
Costs of goods sold		$ (55,400)		(458,528)
Income tax provision		17,058		141,181
Net earnings		$ 38,342		$ 317,347
Basic (in dollars per share)				$ 0.04
Diluted (in dollars per share)				$ 0.04
Change in inventories				$ (458,528)
Change in deferred income taxes				108,483
Change in income taxes payable				$ 32,698
Inventories					7,290,102
Deferred income tax liability					1,768,968
Retained earnings					$ 5,521,134
Restatement Adjustment [Member] | Difference Between LIFO and Average Cost Method [Member]
Income tax provision	(329,384)		610,626
Net earnings	$ (1,022,794)		$ 1,895,968
Basic (in dollars per share)	$ (0.15)		$ 0.27
Diluted (in dollars per share)	$ (0.15)		$ 0.27
Earnings before income taxes	$ (1,352,177)		$ 2,506,595