Statements of Cash Flows - USD ($)	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
OPERATING ACTIVITIES
Net income	$ 11,694,384	$ 14,526,642
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	542,926	549,969
Stock-based compensation	45,572	48,360
Deferred income taxes	(129,155)	77,779
Changes in operating assets and liabilities:
Accounts receivable	729,737	301,620
Inventories	(16,327)	380,426
Prepaid expenses and other assets	391,699	(394,504)
Accounts payable and accrued expenses	105,996	405,481
Net cash provided by operating activities	13,364,832	15,895,773
INVESTING ACTIVITIES
Purchases of fixed assets	(62,727)	(52,041)
Purchases of marketable securities	(10,512,400)	(7,196,330)
Proceeds from maturities and sales of marketable securities	19,000,000	12,500,000
Net cash provided by investing activities	8,424,873	5,251,629
FINANCING ACTIVITIES
Proceeds from exercise of stock options		112,360
Repurchase of common stock	(91,419)	(687,432)
Payment of dividends to shareholders	(19,336,540)	(19,384,040)
Net cash used in financing activities	(19,427,959)	(19,959,112)
Increase in cash and cash equivalents	2,361,746	1,188,290
Cash and cash equivalents at beginning of year	8,065,594	6,877,304
Cash and cash equivalents at end of year	10,427,340	8,065,594
Supplemental disclosures of cash flow information:
Cash paid during the year for income taxes	$ 2,438,788	$ 2,586,661