Statements of Cash Flows - USD ($)	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
OPERATING ACTIVITIES
Net income	$ 12,292,315	$ 14,368,354	$ 11,135,875
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	850,970	934,371	844,339
Stock-based compensation	21,160	58,960	53,200
Excess tax benefits	(352,294)	(24,288)	(57,472)
Deferred income taxes	295,827	155,713	121,881
Changes in operating assets and liabilities
Accounts receivable	719,888	(632,400)	189,821
Inventories	537,259	(535,159)	129,259
Prepaid expenses and other assets	(159,611)	241,363	141,871
Accounts payable and accrued expenses	(611,290)	$ 303,152	$ (157,350)
Deferred revenue	714,805
Net cash provided by operating activities	14,309,029	$ 14,870,066	$ 12,401,424
INVESTING ACTIVITIES
Purchases of fixed assets	(287,275)	(185,007)	(160,718)
Purchases of marketable securities	(14,568,089)	(8,997,086)	(22,753,916)
Proceeds from maturities of marketable securities	19,725,000	12,160,000	10,055,000
Net cash provided by (used in) investing activities	4,869,636	2,977,907	(12,859,634)
FINANCING ACTIVITIES
Proceeds from sale of common stock	292,909	302,701	416,760
Excess tax benefits	352,294	$ 24,288	57,472
Repurchase of common stock	(2,311,673)		$ (1,263,405)
Payment of dividends to shareholders	(19,414,864)	$ (10,000,000)
Net cash used in financing activities	(21,081,334)	(9,673,011)	$ (789,173)
(Decrease) increase in cash and cash equivalents	(1,902,669)	8,174,962	(1,247,383)
Cash and cash equivalents at beginning of year	9,437,262	1,262,300	2,509,683
Cash and cash equivalents at end of year	7,534,593	9,437,262	1,262,300
Supplemental disclosures of cash flow information:
Cash paid during the year for income taxes	$ 5,810,000	$ 6,800,000	$ 5,263,033