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	$ 364,493	$ 306,693	$ 706,295	$ 595,025
Cost of sales	236,506	197,173	456,339	383,428
Selling and administrative expenses	70,847	62,060	137,069	122,610
Total operating costs and expenses	307,353	259,233	593,408	506,038
Operating income	57,140	47,460	112,887	88,987
Interest expense	3,541	2,815	6,890	5,806
Other expense (income), net	394	(824)	416	(597)
Income before income taxes	53,205	45,469	105,581	83,778
Income taxes	8,178	12,257	22,251	21,718
Net income	$ 45,027	$ 33,212	$ 83,330	$ 62,060
Per common share:
Basic (in dollars per share)	$ 0.83	$ 0.61	$ 1.54	$ 1.14
Diluted (in dollars per share)	0.82	0.61	1.52	1.14
Dividends (in dollars per share)	$ 0.14	$ 0.13	$ 0.27	$ 0.25
Weighted average common shares outstanding:
Basic (in shares)	54,177,251	54,168,562	54,178,185	54,207,145
Diluted (in shares)	54,722,211	54,642,071	54,686,172	54,662,389