Statements of Shareholders Equity (USD $)	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Balance at Mar. 31, 2012	$ 48,247	$ 20,974,477	$ 1,087,456	$ 59,348,678	$ 81,458,858
Balance, shares at Mar. 31, 2012	4,824,745
Exercise of stock options and warrants	377	143,811	0	0	144,188
Exercise of stock options and warrants, shares	37,691
Comprehensive income:
Unrealized gain (loss) on marketable securities, net of tax	0	0	470,270	0	470,270
Net income				11,828,838	11,828,838
Comprehensive income					12,299,108
Stock-based compensation	0	66,720	0	0	66,720
Tax benefit of stock-based compensation		15,734			15,734
Balance at Mar. 31, 2013	48,624	21,200,742	1,557,726	71,177,516	93,984,608
Balance, Shares at Mar. 31, 2013	4,862,436
Exercise of stock options and warrants	140	416,620	0	0	416,760
Exercise of stock options and warrants, shares	14,000
Repurchase of common stock	(254)	(1,263,151)			(1,263,405)
Repurchase of common stock, shares	(25,393)
Comprehensive income:
Unrealized gain (loss) on marketable securities, net of tax	0	0	(679,869)		(679,869)
Net income	0	0	0	11,135,875	11,135,875
Comprehensive income					10,456,006
Stock-based compensation		53,200			53,200
Tax benefit of stock-based compensation		57,472			57,472
Balance at Mar. 31, 2014	48,510	20,464,883	877,857	82,313,391	103,704,641
Balance, Shares at Mar. 31, 2014	4,851,043
Exercise of stock options and warrants	70	302,631	0	0	302,701
Exercise of stock options and warrants, shares	6,910
Comprehensive income:
Unrealized gain (loss) on marketable securities, net of tax	0	0	(131,410)		(131,410)
Net income	0	0	0	14,368,354	14,368,354
Comprehensive income					14,236,944
Stock-based compensation		58,960			58,960
Tax benefit of stock-based compensation		24,288			24,288
Cash dividends declared ($2.06 per share of common stock)				(10,000,000)	(10,000,000)
Balance at Mar. 31, 2015	$ 48,580	$ 20,850,762	$ 746,447	$ 86,681,745	$ 108,327,534
Balance, Shares at Mar. 31, 2015	4,857,953