Condensed Consolidated Statements of Income - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net sales		$ 88,252	$ 85,753	$ 176,208	$ 172,922
Cost of sales	[1]	68,811	66,928	137,816	135,056
Gross profit		19,441	18,825	38,392	37,866
Selling, general and administrative expenses (SG&A)		8,309	8,311	16,871	15,960
Operating income		11,132	10,514	21,521	21,906
Equity method investment loss		0	(819)	0	(348)
Interest expense, net		(289)	(379)	(496)	(710)
Income before income taxes		10,843	9,316	21,025	20,848
Income tax expense		3,316	2,947	4,571	5,801
Net income		7,527	6,369	16,454	15,047
Income attributable to participating securities		148	183	323	433
Net income attributable to common shareholders and used in EPS calculation		$ 7,379	$ 6,186	$ 16,131	$ 14,614
Share information:
Basic and diluted weighted average common shares (in shares)		16,869,481	16,745,679	16,856,423	16,727,305
Basic and diluted earnings per common share (in dollars per share)		$ 0.44	$ 0.37	$ 0.96	$ 0.87
Dividends and dividend equivalents per common share (in dollars per share)		$ 0.08	$ 0.04	$ 0.16	$ 0.08

[1] Includes related party purchases of $0 and $9,180 for the quarters ended June 30, 2018 and 2017, respectively. Includes related party purchases of $0 and $18,425 for the year-to-date periods ended June 30, 2018 and 2017, respectively.