Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net sales	$ 366,660	$ 341,802
Cost of sales	237,134	219,549
Selling and administrative expenses	72,893	65,975
Total operating costs and expenses	310,027	285,524
Operating income	56,633	56,278
Interest expense	3,892	3,349
Other expense (income), net	1,763	553
Income before income taxes	50,978	52,376
Income taxes	12,160	14,073
Net income	$ 38,818	$ 38,303
Per common share:
Basic (in dollars per share)	$ 0.73	$ 0.71
Diluted (in dollars per share)	0.72	0.70
Dividends (in dollars per share)	$ 0.14	$ 0.13
Weighted average common shares outstanding:
Basic (in shares)	53,535,424	54,179,130
Diluted (in shares)	54,089,327	54,651,835