Consolidated Statements of Stockholders' Equity - USD ($)	Common Stock [Member]	Additional Paid in Capital [Member]	Retained Earning [Member]	Treasury Stock [Member]	Total
Balances at Dec. 31, 2014	$ 7,062	$ 25,059,458	$ 9,620,978	$ (4,430,643)	$ 30,256,855
Balances (in shares) at Dec. 31, 2014	7,062,209
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon stock option exercise	$ 228	2,823,755	0	0	2,823,983
Issuance of common stock upon stock option exercise (in shares)	227,958
Stock compensation expense	$ 0	105,782	0	0	105,782
Repurchases of common stock	0	0	0	(1,802,466)	(1,802,466)
Excess tax benefits from share-based payment arrangements	0	3,808,423	0	0	3,808,423
Net income	0	0	9,617,632	0	9,617,632
Balances at Dec. 31, 2015	$ 7,290	31,797,418	19,238,610	(6,233,109)	44,810,209
Balances (in shares) at Dec. 31, 2015	7,290,167
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon stock option exercise	$ 265	711,135	0	0	711,400
Issuance of common stock upon stock option exercise (in shares)	265,000
Stock compensation expense	$ 0	133,904	0	0	133,904
Repurchases of common stock	0	0	0	(1,048,592)	(1,048,592)
Excess tax benefits from share-based payment arrangements	0	302,783	0	0	302,783
Net income	0	0	11,372,239	0	11,372,239
Balances at Dec. 31, 2016	$ 7,555	32,945,240	30,610,849	(7,281,701)	$ 56,281,943
Balances (in shares) at Dec. 31, 2016	7,555,167				7,156,281
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon stock option exercise	$ 45	395,705	0	0	$ 395,750
Issuance of common stock upon stock option exercise (in shares)	45,000
Stock compensation expense	$ 0	127,378	0	0	127,378
Repurchases of common stock	0	0	0	(616,499)	(616,499)
Net income	0	0	11,328,266	0	11,328,266
Balances at Dec. 31, 2017	$ 7,600	$ 33,468,323	$ 41,939,115	$ (7,898,200)	$ 67,516,838
Balances (in shares) at Dec. 31, 2017	7,600,167				7,189,233