Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales	$ 369,797	$ 357,156	$ 1,111,772	$ 1,063,451
Cost of sales	236,880	235,406	711,622	697,493
Selling and administrative expenses	73,854	72,852	220,575	210,023
Total operating costs and expenses	310,734	308,258	932,197	907,516
Operating income	59,063	48,898	179,575	155,935
Interest expense	4,054	3,748	12,078	10,638
Other expense (income), net	2,447	1,469	5,157	(3,965)
Income before income taxes	52,562	43,681	162,340	149,262
Income taxes	13,453	8,348	34,983	30,599
Net income	$ 39,109	$ 35,333	$ 127,357	$ 118,663
Per common share:
Basic (in dollars per share)	$ 0.76	$ 0.65	$ 2.42	$ 2.19
Diluted (in dollars per share)	0.75	0.65	2.40	2.17
Dividends (in dollars per share)	$ 0.16	$ 0.14	$ 0.46	$ 0.41
Weighted average common shares outstanding:
Basic (in shares)	51,569,764	54,066,509	52,555,130	54,140,551
Diluted (in shares)	52,080,676	54,570,677	53,091,468	54,649,723