Quarterly Data - Quarterly Data (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 31,130,000	$ 34,731,000	$ 39,751,000	$ 31,709,000	$ 30,171,000	$ 33,785,000	$ 38,849,000	$ 27,745,000	$ 137,321,395	$ 130,550,349
Cost of goods sold	19,767,000	22,281,000	25,039,000	19,585,000	19,545,000	21,559,000	24,366,000	17,181,000	86,672,413	82,651,076
Gross profit	11,363,000	12,450,000	14,712,000	12,124,000	10,626,000	12,226,000	14,483,000	10,564,000	50,648,982	47,899,273
Net income	$ 591,000	$ 807,000	$ 2,436,000	$ 764,000	$ (655,000)	$ 1,202,000	$ 2,846,000	$ 659,000	$ 4,598,350	$ 4,052,479
Basic earnings per share	$ .18	$ .24	$ .72	$ .23	$ (.20)	$ .36	$ .85	$ .20	$ 1.36	$ 1.21
Diluted earnings per share	.19	.23	.67	.21	(.16)	.32	.75	.18	1.3	1.09
Dividends per share	$ .12	$ .11	$ .11	$ .11	$ .11	$ .11	$ .11	$ .10	$ .45	$ .43