Statements of Shareholders' Equity (Unaudited) - USD ($)
Cumulative Effect, Period of Adoption, Adjustment [Member]
Common Stock [Member]
Common Stock [Member]
Additional Paid-in Capital [Member]
AOCI Attributable to Parent [Member]
Retained Earnings [Member]
Total
Unrealized (loss) gain from marketable securities, net of tax   $ 570,063 $ 570,063
Net income         3,607,419 3,607,419
Total comprehensive income           4,177,482
Cash dividends declared ($1.00 per share of common stock)         (4,846,010) (4,846,010)
Balance (in shares) at Mar. 31, 2019   4,846,010        
Balance at Mar. 31, 2019   $ 48,460 19,910,558 (82,725) 62,903,918 82,780,211
Balance (in shares) at Jun. 30, 2019   4,846,010        
Balance at Jun. 30, 2019   $ 48,460 19,910,558 487,338 61,665,327 82,111,683
Unrealized (loss) gain from marketable securities, net of tax           748,779
Net income           7,429,481
Balance (in shares) at Mar. 31, 2019   4,846,010        
Balance at Mar. 31, 2019   $ 48,460 19,910,558 (82,725) 62,903,918 82,780,211
Balance (in shares) at Sep. 30, 2019   4,846,010        
Balance at Sep. 30, 2019   $ 48,460 19,958,918 666,054 60,641,379 81,314,811
Unrealized (loss) gain from marketable securities, net of tax   178,716 178,716
Net income         3,822,062 3,822,062
Total comprehensive income           4,000,778
Stock-based compensation   48,360 48,360
Cash dividends declared ($1.00 per share of common stock)         (4,846,010) (4,846,010)
Balance (in shares) at Jun. 30, 2019   4,846,010        
Balance at Jun. 30, 2019   $ 48,460 19,910,558 487,338 61,665,327 82,111,683
Balance (in shares) at Sep. 30, 2019   4,846,010        
Balance at Sep. 30, 2019   $ 48,460 19,958,918 666,054 60,641,379 81,314,811
Unrealized (loss) gain from marketable securities, net of tax   1,242,662 1,242,662
Net income         2,411,865 2,411,865
Total comprehensive income           3,654,527
Stock-based compensation   2,707 2,707
Cash dividends declared ($1.00 per share of common stock)         (4,835,038) (4,835,038)
Balance at Mar. 31, 2020 [1]           77,995,349
Balance (in shares) at Jun. 30, 2020   4,835,038        
Balance at Jun. 30, 2020   $ 48,350 19,386,663 1,759,185 55,623,347 76,817,545
Unrealized (loss) gain from marketable securities, net of tax           1,112,338
Net income           4,634,205
Balance at Mar. 31, 2020 [1]           77,995,349
Balance (in shares) at Sep. 30, 2020 4,833,232          
Balance at Sep. 30, 2020   48,332 19,329,577 1,628,861 53,010,649 74,017,419
Unrealized (loss) gain from marketable securities, net of tax   (130,324) (130,324)
Net income   2,222,340 2,222,340
Total comprehensive income   2,092,016
Stock-based compensation   34,315 34,315
Cash dividends declared ($1.00 per share of common stock)   (4,835,038) (4,835,038)
Balance (in shares) at Jun. 30, 2020   4,835,038        
Balance at Jun. 30, 2020   $ 48,350 19,386,663 1,759,185 55,623,347 76,817,545
Repurchase of common stock (in shares)   (1,806)        
Repurchase of common stock   $ (18) (91,401) (91,419)
Balance (in shares) at Sep. 30, 2020 4,833,232          
Balance at Sep. 30, 2020   $ 48,332 $ 19,329,577 $ 1,628,861 $ 53,010,649 $ 74,017,419
[1] The March 31, 2020 Balance Sheet is derived from the audited financial statements contained in our Annual Report on Form 10-K for the fiscal year ended March 31, 2020.