Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
OPERATING ACTIVITIES
Net income	$ 10,030,252	$ 9,921,486
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	726,842	868,218
Stock-based compensation	40,920	22,000
Excess tax deficiencies		293
Deferred income taxes	153,954	(61,076)
Changes in operating assets and liabilities:
Accounts receivable	1,270,936	782,427
Inventories	(238,028)	42,755
Prepaid expenses and other assets	(360,675)	(16,909)
Accounts payable and accrued expenses	(159,525)	162,906
Deferred revenue	(142,733)	(714,805)
Net cash provided by operating activities	11,321,943	11,007,295
INVESTING ACTIVITIES
Purchases of fixed assets	(604,755)	(200,447)
Purchases of marketable securities	(16,256,210)	(11,528,240)
Proceeds from maturities of marketable securities	16,540,000	11,400,000
Net cash used in investing activities	(320,965)	(328,687)
FINANCING ACTIVITIES
Proceeds from sale of common stock	51,040	92,310
Excess tax (deficiencies)		(293)
Payment of dividends to shareholders	(14,523,030)	(14,506,030)
Net cash used in financing activities	(14,471,990)	(14,414,013)
Decrease in cash and cash equivalents	(3,471,012)	(3,735,405)
Cash and cash equivalents at beginning of period	8,199,364	7,534,593
Cash and cash equivalents at end of period	4,728,352	3,799,188
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	$ 4,615,019	$ 4,720,000