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
Unrealized (loss) gain from marketable securities, net of tax					$ 570,063		$ 570,063
Net income						3,607,419	3,607,419
Total comprehensive income							4,177,482
Cash dividends declared ($1.00 per share of common stock)						(4,846,010)	(4,846,010)
Balance (in shares) at Mar. 31, 2019			4,846,010
Balance at Mar. 31, 2019			$ 48,460	19,910,558	(82,725)	62,903,918	82,780,211
Balance (in shares) at Jun. 30, 2019			4,846,010
Balance at Jun. 30, 2019			$ 48,460	19,910,558	487,338	61,665,327	82,111,683
Unrealized (loss) gain from marketable securities, net of tax							748,779
Net income							7,429,481
Balance (in shares) at Mar. 31, 2019			4,846,010
Balance at Mar. 31, 2019			$ 48,460	19,910,558	(82,725)	62,903,918	82,780,211
Balance (in shares) at Sep. 30, 2019			4,846,010
Balance at Sep. 30, 2019			$ 48,460	19,958,918	666,054	60,641,379	81,314,811
Unrealized (loss) gain from marketable securities, net of tax					178,716		178,716
Net income						3,822,062	3,822,062
Total comprehensive income							4,000,778
Stock-based compensation				48,360			48,360
Cash dividends declared ($1.00 per share of common stock)						(4,846,010)	(4,846,010)
Balance (in shares) at Jun. 30, 2019			4,846,010
Balance at Jun. 30, 2019			$ 48,460	19,910,558	487,338	61,665,327	82,111,683
Balance (in shares) at Sep. 30, 2019			4,846,010
Balance at Sep. 30, 2019			$ 48,460	19,958,918	666,054	60,641,379	81,314,811
Unrealized (loss) gain from 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 at Mar. 31, 2020	[1]						77,995,349
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) gain from marketable securities, net of tax							1,112,338
Net income							4,634,205
Balance at Mar. 31, 2020	[1]						77,995,349
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) gain from 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)
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
Repurchase of common stock (in shares)			(1,806)
Repurchase of common stock			$ (18)	(91,401)			(91,419)
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

[1] The March 31, 2020 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, 2020.