Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	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	Dec. 31, 2017
Selected quarterly financial data [Abstract]
Net sales	$ 213,837	$ 209,320	$ 191,893	$ 187,242	$ 208,968	$ 210,547	$ 198,775	$ 199,442	$ 802,291	$ 817,733	$ 819,866
Gross profit	115,830	112,019	103,557	103,083	114,466	115,372	107,797	108,907	434,488	446,542	444,923
Income before taxes	7,592	8,169	8,237	4,725	12,338	11,204	8,410	8,457	28,724	40,408	43,223
Net income	6,100	$ 6,097	$ 6,046	$ 3,621	$ 9,429	$ 8,352	$ 6,214	$ 6,313	21,865	30,307	21,075
Diluted net earnings per share [Abstract]
Impairment loss related to retail store	2,415									0	0
Leases	$ (418)								$ (418)	$ 0	$ 0
Common Stock [Member]
Basic net earnings per share [Abstract]
Common stock (in dollars per share)	$ 0.32	$ 0.31	$ 0.30	$ 0.18	$ 0.46	$ 0.40	$ 0.30	$ 0.30	$ 1.10	$ 1.45	$ 1.00
Diluted net earnings per share [Abstract]
Common stock (in dollars per share)	0.31	0.31	0.29	0.17	0.45	0.39	0.29	0.29	1.08	1.42	0.98
Class A Common Stock [Member]
Basic net earnings per share [Abstract]
Common stock (in dollars per share)	0.30	0.30	0.28	0.17	0.44	0.38	0.28	0.28	1.04	1.39	0.95
Diluted net earnings per share [Abstract]
Common stock (in dollars per share)	$ 0.30	$ 0.30	$ 0.27	$ 0.17	$ 0.45	$ 0.38	$ 0.28	$ 0.28	$ 1.03	$ 1.39	$ 0.94