Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net sales	$ 375,315	$ 364,493	$ 741,975	$ 706,295
Cost of sales	237,608	242,538	474,742	462,087
Selling and administrative expenses	73,828	71,196	146,721	137,171
Total operating costs and expenses	311,436	313,734	621,463	599,258
Operating income	63,879	50,759	120,512	107,037
Interest expense	4,133	3,541	8,025	6,890
Other expense (income), net	947	(5,987)	2,710	(5,434)
Income before income taxes	58,799	53,205	109,777	105,581
Income taxes	9,370	8,178	21,530	22,251
Net income	$ 49,429	$ 45,027	$ 88,247	$ 83,330
Per common share:
Basic (in dollars per share)	$ 0.94	$ 0.83	$ 1.66	$ 1.54
Diluted (in dollars per share)	0.93	0.82	1.65	1.52
Dividends (in dollars per share)	$ 0.16	$ 0.14	$ 0.30	$ 0.27
Weighted average common shares outstanding:
Basic (in shares)	52,581,804	54,177,251	53,055,980	54,178,185
Diluted (in shares)	53,135,742	54,722,211	53,608,447	54,686,172