Consolidated Statements of Stockholders' Equity - USD ($)	Total	Common stock [Member]	Additional paid-in capital [Member]	Retained earnings [Member]	Treasury stock [Member]
Balance (shares) at Dec. 31, 2015		27,813,772
Balance at Dec. 31, 2015	$ 35,250,813	$ 2,781,377	$ 18,481,683	$ 15,295,940	$ (1,308,187)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 12,999,749	$ 0	0	12,999,749	0
Balance (shares) at Dec. 31, 2016	25,451,354	27,813,772
Balance at Dec. 31, 2016	$ 48,250,562	$ 2,781,377	18,481,683	28,295,689	(1,308,187)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 8,297,751	$ 0	0	8,297,751	0
Balance (shares) at Dec. 31, 2017	25,451,354	27,813,772
Balance at Dec. 31, 2017	$ 56,548,313	$ 2,781,377	$ 18,481,683	$ 36,593,440	$ (1,308,187)