Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Net sales	$ 101,326	$ 102,319	$ 187,404	$ 187,741
Cost of sales	69,648	69,572	130,740	129,263
Gross profit	31,678	32,747	56,664	58,478
Selling, general and administrative expenses	11,971	10,561	22,501	19,474
Loss (gain) on disposal of assets	48	(12)	47	(20)
Income from operations	19,659	22,198	34,116	39,024
Interest income, net	71	67	131	141
Other income, net	34	10	45	127
Income before taxes	19,764	22,275	34,292	39,292
Income tax provision	5,970	7,550	10,281	13,016
Net income	$ 13,794	$ 14,725	$ 24,011	$ 26,276
Earnings per share:
Basic (usd per share)	$ 0.26	$ 0.28	$ 0.46	$ 0.47
Diluted (usd per share)	0.26	0.27	0.45	0.47
Cash dividends declared per common share	$ 0.13	$ 0.11	$ 0.13	$ 0.11
Weighted average shares outstanding:
Basic (in shares)	52,615,366	53,036,009	52,624,782	53,028,224
Diluted (in shares)	53,151,134	53,574,702	53,176,425	53,563,676