Statement of Stockholders' Equity - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Comprehensive income:
Balance as of March 31, 2014 (in shares)	4,862,436
Balance as of March 31, 2013 (in shares) at Mar. 31, 2013	4,862,436
Balance as of March 31, 2013 at Mar. 31, 2013	$ 48,624	$ 21,200,742	$ 1,557,726	$ 71,177,516	$ 93,984,608
Exercise of stock options (in shares)	14,000
Exercise of stock options	$ 140	416,620			416,760
Repurchase of common stock (in shares)	(25,393)
Repurchase of common stock	$ (254)	$ (1,263,151)			(1,263,405)
Comprehensive income:
Unrealized loss from marketable securities, net of tax			$ (679,869)		(679,869)
Net income				$ 11,135,875	11,135,875
Total comprehensive income					10,456,006
Stock-based compensation		$ 53,200			53,200
Tax benefit of stock- based compensation		57,472			57,472
Balance as of March 31, 2014 (in shares)	4,862,436
Balance as of March 31, 2014 at Mar. 31, 2014	$ 48,510	20,464,883	$ 877,857	$ 82,313,391	103,704,641
Comprehensive income:
Exercise of stock options (in shares)	14,000
Exercise of stock options	$ 140	416,620			416,760
Balance as of March 31, 2015 (in shares) at Mar. 31, 2014	4,851,043
Comprehensive income:
Repurchase of common stock (in shares)	(25,393)
Repurchase of common stock	$ (254)	(1,263,151)			(1,263,405)
Balance as of March 31, 2014 (in shares)	4,851,043
Exercise of stock options (in shares)	6,910
Exercise of stock options	$ 70	$ 302,631			302,701
Repurchase of common stock					0
Unrealized loss from marketable securities, net of tax			$ (131,410)		(131,410)
Net income				$ 14,368,354	14,368,354
Total comprehensive income					14,236,944
Stock-based compensation		$ 58,960			58,960
Tax benefit of stock- based compensation		24,288			24,288
Balance as of March 31, 2014 (in shares)	4,851,043
Balance as of March 31, 2014 at Mar. 31, 2015	$ 48,580	20,850,762	$ 746,447	$ 86,681,745	108,327,534
Comprehensive income:
Exercise of stock options (in shares)	6,910
Exercise of stock options	$ 70	$ 302,631			302,701
Cash dividends declared ($2.06 per share of common stock)				$ (10,000,000)	(10,000,000)
Balance as of March 31, 2015 (in shares) at Mar. 31, 2015	4,857,953
Comprehensive income:
Repurchase of common stock					0
Balance as of March 31, 2014 (in shares)	4,857,953
Exercise of stock options (in shares)	18,090
Exercise of stock options	$ 181	$ 292,728			292,909
Repurchase of common stock (in shares)	(41,033)
Repurchase of common stock	$ (411)	$ (2,311,262)			(1,695,788)
Unrealized loss from marketable securities, net of tax			$ (295,088)		(295,088)
Net income				$ 12,292,315	12,292,315
Total comprehensive income					11,997,227
Stock-based compensation		$ 21,160			21,160
Tax benefit of stock- based compensation		352,294			352,294
Balance as of March 31, 2014 (in shares)	4,857,953
Balance as of March 31, 2014 at Mar. 31, 2016	$ 48,350	19,205,682	$ 451,359	$ 79,559,196	99,264,587
Comprehensive income:
Exercise of stock options (in shares)	18,090
Exercise of stock options	$ 181	$ 292,728			292,909
Cash dividends declared ($2.06 per share of common stock)				$ (19,414,864)	(19,414,864)
Balance as of March 31, 2015 (in shares) at Mar. 31, 2016	4,835,010
Comprehensive income:
Repurchase of common stock (in shares)	(41,033)
Repurchase of common stock	$ (411)	$ (2,311,262)			$ (1,695,788)
Balance as of March 31, 2014 (in shares)	4,835,010