Consolidated Statements of Income - USD ($) $ 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
Income Statement [Abstract]
Net sales	$ 122,574	$ 113,500	$ 119,437	$ 113,822	$ 112,340	$ 112,937	$ 109,588	$ 99,082	$ 469,333	$ 433,947	$ 405,232
Cost of sales		86,090	89,233	88,392	84,494	80,107	81,927	83,886	349,908	330,414	281,581
Gross profit	36,381	27,410	30,204	25,430	27,846	32,830	27,661	15,196	119,425	103,533	123,651
Selling, general and administrative expenses		12,374	12,912	13,677	10,723	12,667	13,153	11,651	52,077	48,194	49,371
Loss (gain) on disposal of assets		6	6	284	(3)	2	(4)	(7)	337	(12)	45
Income from operations		15,030	17,286	11,469	17,126	20,161	14,512	3,552	67,011	55,351	74,235
Interest income, net		9	31	9	25	36	67	68	66	196	298
Other (expense) income, net		(7)	17	(26)	(58)	5	12	(6)	(46)	(47)	91
Income before taxes		15,032	17,334	11,452	17,093	20,202	14,591	3,614	67,031	55,500	74,624
Income tax provision		742	3,943	2,695	4,129	5,688	2,894	460	13,320	13,171	20,794
Net income	$ 17,273	$ 14,290	$ 13,391	$ 8,757	$ 12,964	$ 14,514	$ 11,697	$ 3,154	$ 53,711	$ 42,329	$ 53,830
Earnings per share:
Basic (usd per share)	$ 0.33	$ 0.27	$ 0.26	$ 0.17	$ 0.25	$ 0.28	$ 0.22	$ 0.06	$ 1.03	$ 0.81	$ 1.02
Diluted (usd per share)	$ 0.33	$ 0.26	0.26	$ 0.17	0.25	$ 0.27	0.22	$ 0.06	1.02	0.80	1.01
Cash dividends declared per common share (in dollars per share)			$ 0.16		$ 0.16		$ 0.16		$ 0.32	$ 0.32	$ 0.26
Weighted average shares outstanding:
Basic (in shares)		52,111,444	52,120,272	51,992,150	52,086,247	52,238,796	52,383,842	52,433,902	52,079,865	52,284,616	52,572,496
Diluted (in shares)		52,722,127	52,474,199	52,369,660	52,420,529	52,627,541	52,717,787	52,910,223	52,635,415	52,667,939	53,078,734