Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Net sales	$ 113,668	$ 104,568	$ 301,072	$ 292,309
Cost of sales	78,010	71,476	208,750	200,739
Gross profit	35,658	33,092	92,322	91,570
Selling, general and administrative expenses	13,034	10,400	35,535	29,874
Loss (gain) on disposal of assets	(1)	0	46	(20)
Income from operations	22,625	22,692	56,741	61,716
Interest income, net	84	82	215	223
Other income, net	41	(12)	86	115
Income before taxes	22,750	22,762	57,042	62,054
Income tax provision	8,033	7,080	18,314	20,098
Net income	$ 14,717	$ 15,682	$ 38,728	$ 41,956
Earnings per share:
Basic (usd per share)	$ 0.28	$ 0.30	$ 0.74	$ 0.79
Diluted (usd per share)	0.28	0.29	0.73	0.78
Cash dividends declared per common share	$ 0	$ 0	$ 0.13	$ 0.11
Weighted average shares outstanding:
Basic (in shares)	52,566,619	52,891,879	52,586,429	52,942,571
Diluted (in shares)	53,014,269	53,394,331	53,103,408	53,467,023