Quarterly Financial Information (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
Quarterly Financial Information (unaudited)
Net sales	$ 160,298	$ 141,869	$ 176,356	$ 93,187	$ 151,825	$ 124,832	$ 163,446	$ 83,964	$ 571,710	$ 524,067	$ 474,927
Gross profit	46,339	39,939	59,593	22,946	44,094	34,920	55,849	20,027	168,817	154,890	143,086
Income (loss) before taxes	14,062	15,542	33,773	(760)	19,748	11,069	28,080	(3,138)	62,617	55,759	52,915
Net income (loss)	$ 11,560	$ 12,429	$ 25,474	$ (297)	$ 14,696	$ 9,921	$ 21,164	$ (1,876)	$ 48,527	$ 43,321	$ 54,609
Basic gain per common share (in dollars per share)	$ 0.50	$ 0.54	$ 1.10	$ (0.01)	$ 0.64	$ 0.43	$ 0.92	$ (0.08)	$ 2.13	$ 1.91	$ 2.42
Gain per common share assuming dilution (in dollars per share)	0.50	0.53	1.10	(0.01)	0.63	0.43	0.91	(0.08)	$ 2.11	$ 1.89	$ 2.40
Cash dividends paid per share (in dollars per share)	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.27