Statements Of Cash Flows (USD $)	6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
OPERATING ACTIVITIES
Net income	$ 5,796,476	$ 5,820,541
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	380,272	291,531
Stock-based compensation	53,200	66,720
Excess tax benefits	0	(2,383)
Deferred income taxes	28,457	14,265
Changes in operating assets and liabilities:
Accounts receivable	(509,632)	723,158
Inventories	236,147	(293,112)
Prepaid expenses and other assets	63,341	(127,903)
Accounts payable and accrued expenses	(54,230)	(60,556)
Net cash provided by operating activities	5,994,031	6,432,261
INVESTING ACTIVITIES
Purchases of fixed assets	0	(1,019,269)
Purchases of marketable securities	(11,533,738)	(11,979,769)
Proceeds from maturities and sales of marketable securities	5,855,000	6,885,000
Net cash used in investing activities	(5,678,738)	(6,114,038)
FINANCING ACTIVITIES
Net proceeds from sale of common stock	0	69,420
Excess tax benefits	0	2,383
Repurchase of common stock	(1,263,405)	0
Net cash provided by financing activities	(1,263,405)	71,803
Increase in cash and cash equivalents	(948,112)	390,026
Cash and cash equivalents at beginning of period	2,509,683	1,544,536
Cash and cash equivalents at end of period	1,561,571	1,934,562
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	$ 2,838,033	$ 2,920,000