Quarterly Data - Quarterly Data (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 33,872,000	$ 36,995,000	$ 40,220,000	$ 31,370,000	$ 31,130,000	$ 34,731,000	$ 39,751,000	$ 31,709,000	$ 142,457,342	$ 137,321,395
Cost of goods sold	21,578,000	23,861,000	25,449,000	19,568,000	19,767,000	22,281,000	25,039,000	19,585,000	90,456,484	86,672,413
Gross profit	12,294,000	13,134,000	14,771,000	11,802,000	11,363,000	12,450,000	14,712,000	12,124,000	52,000,858	50,648,982
Net income	$ 978,000	$ 1,059,000	$ 2,671,000	$ 807,000	$ 591,000	$ 807,000	$ 2,436,000	$ 764,000	$ 5,513,608	$ 4,598,350
Basic earnings per share	$ 0.29	$ 0.32	$ 0.80	$ 0.24	$ 0.18	$ 0.24	$ 0.72	$ 0.23	$ 1.65	$ 1.36
Diluted earnings per share	0.29	0.30	0.77	0.24	0.17	0.23	0.67	0.21	1.60	1.30
Dividends per share	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.11	$ 0.11	$ 0.11	$ 0.48	$ 0.45