Statements of Shareholders' Equity - USD ($)	Cumulative Effect, Period of Adoption, Adjustment [Member] Common Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Mar. 31, 2020		4,835,038
Balance at Mar. 31, 2020		$ 48,350	$ 19,383,956	$ 516,523	$ 58,046,520	$ 77,995,349
Repurchase of common stock (in shares)		(1,806)
Repurchase of common stock		$ (18)	(91,401)			(91,419)
Unrealized gain (loss) from marketable securities, net of tax				584,596		584,596
Net income					11,694,384	11,694,384
Total comprehensive income						12,278,980
Stock-based compensation			45,572			45,572
Cash dividends declared ($4.00 per share of common stock)					(19,336,540)	(19,336,540)
Balance (in shares) at Mar. 31, 2021	4,833,232
Balance at Mar. 31, 2021		$ 48,332	19,338,127	1,101,119	50,404,364	70,891,942
Repurchase of common stock (in shares)		(2,888)
Repurchase of common stock		$ (29)	(163,492)			(163,521)
Unrealized gain (loss) from marketable securities, net of tax				(1,419,239)		(1,419,239)
Net income					14,507,501	14,507,501
Total comprehensive income						13,088,262
Stock-based compensation			81,855			81,855
Cash dividends declared ($4.00 per share of common stock)					(19,333,409)	(19,333,409)
Exercise of stock options (in shares)		482
Exercise of stock options		$ 5	(5)
Balance (in shares) at Mar. 31, 2022		4,830,826
Balance at Mar. 31, 2022		$ 48,308	$ 19,256,485	$ (318,120)	$ 45,578,456	$ 64,565,129