Inventories (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Inventories
Raw materials	$ 1,563,864	$ 1,428,924
Work-in-progress	359,337	423,186
Finished goods	1,632,650	1,416,547
Reduction to LIFO cost	(1,187,020)	(1,182,592)
Total inventories	$ 2,368,831	$ 2,086,065