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