Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Net sales	$ 86,078	$ 85,422
Cost of sales	61,092	59,691
Gross profit	24,986	25,731
Selling, general and administrative expenses	10,530	8,913
Gain on disposal of assets	(1)	(8)
Income from operations	14,457	16,826
Interest income, net	60	74
Other income, net	11	117
Income before taxes	14,528	17,017
Income tax provision	4,311	5,466
Net income	$ 10,217	$ 11,551
Earnings per share:
Basic (usd per share)	$ 0.19	$ 0.22
Diluted (usd per share)	0.19	0.22
Cash dividends declared per common share	$ 0	$ 0
Weighted average shares outstanding:
Basic (in shares)	52,622,539	53,061,058
Diluted (in shares)	53,190,057	53,593,269