Note B - Change in Accounting Principle - Change in Accounting Principle From LIFO to Average Cost (Details) - USD ($)	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Apr. 01, 2017
Costs of goods sold	$ 42,000,840	$ 21,539,959
Income Tax Expense (Benefit), Total	1,162,620	144,961
Net earnings	$ 3,599,893	$ 364,330
Basic (in dollars per share)	$ 0.51	$ 0.05
Diluted (in dollars per share)	$ 0.51	$ 0.05
Inventories	$ (14,269,173)	$ (4,777,078)
Change in deferred income taxes		144,961
Inventories	59,598,607		$ 45,329,434
Deferred income tax liability	1,968,330		1,872,166
Retained earnings	40,100,990		36,711,380
Earnings before income taxes	4,762,513	509,291
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	514,128
Net earnings	$ 1,586,312
Basic (in dollars per share)	$ 0.23
Diluted (in dollars per share)	$ 0.23
Earnings before income taxes	$ 2,100,440
Previously Reported [Member]
Costs of goods sold		21,819,846
Income Tax Expense (Benefit), Total		58,784
Net earnings		$ 170,620
Basic (in dollars per share)		$ 0.02
Diluted (in dollars per share)		$ 0.02
Inventories		$ (4,497,191)
Change in deferred income taxes		58,784
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		(279,887)
Income Tax Expense (Benefit), Total		86,177
Net earnings		$ 193,710
Basic (in dollars per share)		$ 0.03
Diluted (in dollars per share)		$ 0.03
Inventories		$ (279,887)
Change in deferred income taxes		$ 86,177
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	648,492
Net earnings	$ 2,013,581
Basic (in dollars per share)	$ 0.28
Diluted (in dollars per share)	$ 0.28
Earnings before income taxes	$ 2,662,073