Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Net sales	$ 102,319	$ 90,275	$ 187,741	$ 167,043
Cost of sales	69,572	63,158	129,263	118,128
Gross profit	32,747	27,117	58,478	48,915
Selling, general and administrative expenses	10,561	9,200	19,474	17,517
Gain on disposal of assets	(12)	(30)	(20)	(25)
Income from operations	22,198	17,947	39,024	31,423
Interest income, net	67	29	141	73
Other income (expense), net	10	27	127	(48)
Income before taxes	22,275	18,003	39,292	31,448
Income tax provision	7,934	6,873	14,145	11,919
Net income	$ 14,341	$ 11,130	$ 25,147	$ 19,529
Earnings per share:
Basic (usd per share)	$ 0.27	$ 0.21	$ 0.47	$ 0.36
Diluted (usd per share)	0.27	0.20	0.47	0.36
Cash dividends declared per common share	$ 0.11	$ 0.11	$ 0.11	$ 0.11
Weighted average shares outstanding:
Basic (in shares)	53,036,009	54,208,362	53,028,224	54,205,657
Diluted (in shares)	53,401,238	54,669,763	53,395,361	54,714,604