Statements of Shareholders' Equity (Unaudited) - USD ($)	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
Comprehensive income:
Unrealized gain (loss) from marketable securities, net of tax			(107,027)		(107,027)
Net income				3,945,049	3,945,049
Total comprehensive income					3,838,022
Cash dividends declared				(4,842,010)	(4,842,010)
Balance (in shares) at Jun. 30, 2018	4,842,010
Balance at Jun. 30, 2018	$ 48,420	19,599,298	(1,083,027)	66,873,061	85,437,752
Comprehensive income:
Cumulative effect of accounting change			(60,365)	60,365
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
Comprehensive income:
Unrealized gain (loss) 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				(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