Inventories (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Inventories
Raw materials	$ 1,624,803	$ 1,428,924
Work-in-progress	428,384	423,186
Finished goods	1,618,978	1,416,547
Reduction to LIFO cost	(1,200,619)	(1,182,592)
Total inventories	$ 2,471,546	$ 2,086,065