Note B - Change in Accounting Principle - Change in Accounting Principle From LIFO to Average Cost (Details) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Apr. 01, 2017
Costs of goods sold	$ 49,487,488	$ 24,577,299	$ 91,488,328	$ 46,117,258
Income Tax Expense (Benefit), Total	644,709	184,927	1,807,329	329,888
Net earnings	$ 2,000,916	$ 395,334	$ 5,600,809	$ 759,664
Basic (in dollars per share)	$ 0.29	$ 0.05	$ 0.80	$ 0.11
Diluted (in dollars per share)	$ 0.29	$ 0.05	$ 0.80	$ 0.11
Inventories			$ (9,317,746)	$ (5,627,744)
Change in deferred income taxes				314,248
Change in income taxes payable			913,139	15,640
Inventories	$ 54,647,180		54,647,180		$ 45,329,434
Deferred income tax liability	1,864,320		1,864,320		1,872,166
Retained earnings	41,681,339		41,681,339		36,711,380
Earnings before income taxes	2,645,625	$ 580,261	7,408,138	1,089,552
Change in Inventory Costing Method from LIFO to Average Cost [Member]
Retained earnings						$ 4,418,318
Computed under LIFO [Member]
Income Tax Expense (Benefit), Total	353,190		867,318
Net earnings	$ 1,095,735		$ 2,682,047
Basic (in dollars per share)	$ 0.16		$ 0.38
Diluted (in dollars per share)	$ 0.16		$ 0.38
Earnings before income taxes	$ 1,448,925		$ 3,549,365
Previously Reported [Member]
Costs of goods sold		24,700,540		46,520,386
Income Tax Expense (Benefit), Total		146,981		205,765
Net earnings		$ 310,039		$ 480,659
Basic (in dollars per share)		$ 0.04		$ 0.07
Diluted (in dollars per share)		$ 0.04		$ 0.07
Inventories				$ (5,224,616)
Change in deferred income taxes				205,765
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		$ (123,241)		(403,128)
Income Tax Expense (Benefit), Total		37,946		124,123
Net earnings		$ 85,295		$ 279,005
Basic (in dollars per share)		$ 0.01		$ 0.04
Diluted (in dollars per share)		$ 0.01		$ 0.04
Inventories				$ (403,128)
Change in deferred income taxes				108,483
Change in income taxes payable				$ 15,640
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 Expense (Benefit), Total	291,519		940,011
Net earnings	$ 905,181		$ 2,918,762
Basic (in dollars per share)	$ 0.13		$ 0.42
Diluted (in dollars per share)	$ 0.13		$ 0.42
Earnings before income taxes	$ 1,196,700		$ 3,858,773