Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 1,436,499	$ 1,230,754	$ 1,193,975
Cost of sales	939,288	790,299	782,817
Selling and administrative expenses	286,933	248,277	242,762
Total operating costs and expenses	1,226,221	1,038,576	1,025,579
Operating income	210,278	192,178	168,396
Interest expense	14,571	11,883	10,698
Other expense (income), net	8	(2,326)	(248)
Income before income taxes	195,699	182,621	157,946
Income taxes	136,284	47,020	36,566
Net income	$ 59,415	$ 135,601	$ 121,380
Per common share:
Basic (in dollars per share)	$ 1.10	$ 2.50	$ 2.21
Diluted (in dollars per share)	1.09	2.48	2.19
Dividends (in dollars per share)	$ 0.55	$ 0.51	$ 0.48
Weighted average common shares outstanding:
Basic (in shares)	54,073,407	54,191,013	55,028,063
Diluted (in shares)	54,605,298	54,631,313	55,513,219