Statements Of Cash Flows (USD $)	6 Months Ended
Sep. 30, 2012	Sep. 30, 2011
OPERATING ACTIVITIES
Net income	$ 5,820,541	$ 5,994,321
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	291,531	235,282
Stock-based compensation	66,720	80,160
Excess tax benefits	(2,383)	0
Deferred income taxes	14,265	(18,861)
Changes in operating assets and liabilities:
Accounts receivable	723,158	624,700
Inventories	(293,112)	(38,171)
Prepaid expenses and other assets	(127,903)	(169,689)
Accounts payable and accrued expenses	(60,556)	(324,240)
Net cash provided by operating activities	6,432,261	6,383,502
INVESTING ACTIVITIES
Purchases of fixed assets	(1,019,269)	(294,234)
Purchases of marketable securities	(11,979,769)	(9,504,221)
Proceeds from maturities and sales of marketable securities	6,885,000	3,786,980
Net cash used in investing activities	(6,114,038)	(6,011,475)
FINANCING ACTIVITIES
Net proceeds from sale of common stock	69,420	0
Excess tax benefits	2,383	0
Net cash provided by financing activities	71,803	0
Increase in cash and cash equivalents	390,026	372,027
Cash and cash equivalents at beginning of period	1,544,536	952,209
Cash and cash equivalents at end of period	1,934,562	1,324,236
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	$ 2,920,000	$ 2,947,565

Name:	us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits are not generally reported as cash and cash equivalents. Includes cash and cash equivalents associated with the entity's continuing operations. Excludes cash and cash equivalents associated with the disposal group (and discontinued operation).