Statements of Shareholders' Equity (Unaudited) - 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
Unrealized loss on marketable securities, net of tax				1,242,662		1,242,662
Net income					2,411,865	2,411,865
Total comprehensive income						3,654,527
Stock-based compensation			2,707			2,707
Cash dividends declared ($1.00 per share of common stock)					(4,835,038)	(4,835,038)
Balance (in shares) at Jun. 30, 2020	4,835,038
Balance at Jun. 30, 2020		$ 48,350	19,386,663	1,759,185	55,623,347	76,817,545
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
Unrealized loss on marketable securities, net of tax						966,886
Net income						8,559,914
Balance (in shares) at Dec. 31, 2020		4,833,232
Balance at Dec. 31, 2020		$ 48,332	19,333,852	1,483,409	52,103,126	72,968,719
Balance (in shares) at Jun. 30, 2020	4,835,038
Balance at Jun. 30, 2020		48,350	19,386,663	1,759,185	55,623,347	76,817,545
Unrealized loss on marketable securities, net of tax				(130,324)		(130,324)
Net income					2,222,340	2,222,340
Total comprehensive income						2,092,016
Stock-based compensation			34,315			34,315
Cash dividends declared ($1.00 per share of common stock)					(4,835,038)	(4,835,038)
Repurchase of common stock (in shares)		(1,806)
Repurchase of common stock		$ (18)	(91,401)			(91,401)
Balance (in shares) at Sep. 30, 2020		4,833,232
Balance at Sep. 30, 2020		$ 48,332	19,329,577	1,628,861	53,010,649	74,017,419
Unrealized loss on marketable securities, net of tax				(145,452)		(145,452)
Net income					3,925,709	3,925,709
Total comprehensive income						3,780,257
Stock-based compensation			4,275			4,275
Cash dividends declared ($1.00 per share of common stock)					(4,833,232)	(4,833,232)
Balance (in shares) at Dec. 31, 2020		4,833,232
Balance at Dec. 31, 2020		$ 48,332	19,333,852	1,483,409	52,103,126	72,968,719
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	[1]
Unrealized loss on marketable securities, net of tax				(90,165)		(90,165)
Net income					3,579,566	3,579,566
Total comprehensive income						3,489,401
Stock-based compensation			7,238			7,238
Cash dividends declared ($1.00 per share of common stock)					(4,833,232)	(4,833,232)
Balance (in shares) at Jun. 30, 2021	4,833,232
Balance at Jun. 30, 2021		$ 48,332	19,345,365	1,010,954	49,150,698	69,555,349
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	[1]
Unrealized loss on marketable securities, net of tax						(667,361)
Net income						10,691,481
Balance (in shares) at Dec. 31, 2021		4,833,714
Balance at Dec. 31, 2021		$ 48,337	19,411,158	433,759	46,596,148	66,489,402
Balance (in shares) at Jun. 30, 2021	4,833,232
Balance at Jun. 30, 2021		48,332	19,345,365	1,010,954	49,150,698	69,555,349
Unrealized loss on marketable securities, net of tax				(197,034)		(197,034)
Net income					3,646,507	3,646,507
Total comprehensive income						3,449,473
Stock-based compensation			56,999			56,999
Cash dividends declared ($1.00 per share of common stock)					(4,833,232)	(4,833,232)
Balance (in shares) at Sep. 30, 2021		4,833,232
Balance at Sep. 30, 2021		$ 48,332	19,402,364	813,920	47,963,973	68,228,589
Unrealized loss on marketable securities, net of tax				(380,161)		(380,161)
Net income					3,465,407	3,465,407
Total comprehensive income						3,085,246
Stock-based compensation			8,799			8,799
Cash dividends declared ($1.00 per share of common stock)					(4,833,232)	(4,833,232)
Exercise of stock options (in shares)		482
Exercise of stock options		$ 5	(5)
Balance (in shares) at Dec. 31, 2021		4,833,714
Balance at Dec. 31, 2021		$ 48,337	$ 19,411,158	$ 433,759	$ 46,596,148	$ 66,489,402

[1] The March 31, 2021 Balance Sheet is derived from the audited financial statements contained in our Annual Report on Form 10-K for the fiscal year ended March 31, 2021.