Statements of Cash Flows (USD $)	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
OPERATING ACTIVITIES
Net income	$ 14,368,354	$ 11,135,875	$ 11,828,838
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	934,371	844,339	647,163
Stock-based compensation	58,960	53,200	66,720
Excess tax benefits	(24,288)	(57,472)	(15,734)
Deferred income taxes	155,713	121,881	51,262
Changes in operating assets and liabilities:
Accounts receivable	(632,400)	189,821	163,445
Inventories	(535,159)	129,259	(107,216)
Prepaid expenses and other assets	241,363	141,871	201,705
Accounts payable and accrued expenses	303,152	(157,350)	(190,881)
Net cash provided by operating activities	14,870,066	12,401,424	12,645,302
INVESTING ACTIVITIES
Purchases of fixed assets	(185,007)	(160,718)	(1,824,324)
Purchases of marketable securities	(8,997,086)	(22,753,916)	(27,209,753)
Proceeds from maturities and sales of marketable securities	12,160,000	10,055,000	17,194,000
Net cash used in investing activities	2,977,907	(12,859,634)	(11,840,077)
FINANCING ACTIVITIES
Proceeds from sale of common stock	302,701	416,760	144,188
Excess tax benefits	24,288	57,472	15,734
Repurchase of common stock	0	(1,263,405)	0
Payment of dividends to shareholders	(10,000,000)	0	0
Net cash provided by financing activities	(9,673,011)	(789,173)	159,922
Increase (decrease) in cash and cash equivalents	8,174,962	(1,247,383)	965,147
Cash and cash equivalents at beginning of period	1,262,300	2,509,683	1,544,536
Cash and cash equivalents at end of period	9,437,262	1,262,300	2,509,683
Supplemental disclosures of cash flow information:
Cash (refunded) paid during the period for income taxes	$ 6,800,000	$ 5,263,033	$ 5,202,616