Statements of Shareholders' Equity - USD ($)	Cumulative Effect, Period of Adoption, Adjustment [Member] Common Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] AOCI Attributable to Parent [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Mar. 31, 2018						4,842,010
Balance at Mar. 31, 2018						$ 48,420	$ 19,599,298	$ (915,635)	$ 67,709,657	$ 86,441,740
Exercise of stock options (in shares)						4,000
Exercise of stock options						$ 40	217,900			217,940
Unrealized gain on marketable securities, net of tax								893,275		893,275
Net income									14,507,936	14,507,936
Total comprehensive income										15,401,211
Stock-based compensation							93,360			93,360
Cash dividends declared									(19,374,040)	(19,374,040)
Balance (in shares) at Mar. 31, 2019	4,846,010
Balance at Mar. 31, 2019			$ (60,365)	$ 60,365		$ 48,460	19,910,558	(82,725)	62,903,918	82,780,211	[1]
Exercise of stock options (in shares)						2,000
Exercise of stock options						$ 20	112,340			112,360
Unrealized gain on marketable securities, net of tax								599,248		599,248
Net income									14,526,642	14,526,642
Total comprehensive income										15,125,890
Stock-based compensation							48,360			48,360
Cash dividends declared									(19,384,040)	(19,384,040)
Repurchase of common stock (in shares)						(12,972)
Repurchase of common stock						$ (130)	(687,302)			(687,432)
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

[1] The March 31, 2019 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, 2019.