Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Net sales	$ 314,941	$ 322,074	$ 615,515	$ 634,173
Cost of sales	204,121	211,705	402,477	426,261
Selling and administrative expenses	60,171	64,988	118,494	127,406
Total operating costs and expenses	264,292	276,693	520,971	553,667
Operating income	50,649	45,381	94,544	80,506
Interest expense	2,586	2,804	5,306	6,123
Other expense (income), net	237	792	318	1,027
Income before income taxes	47,826	41,785	88,920	73,356
Income taxes	13,599	11,557	25,617	20,375
Net income	$ 34,227	$ 30,228	$ 63,303	$ 52,981
Net income
Basic (in dollars per share)	$ 0.62	$ 0.55	$ 1.15	$ 0.97
Diluted (in dollars per share)	0.61	0.54	1.14	0.95
Dividends (in dollars per share)	$ 0.12	$ 0.11	$ 0.24	$ 0.22
Weighted average common shares outstanding:
Basic (in shares)	55,134,890	54,740,750	55,111,019	54,695,865
Diluted (in shares)	55,695,258	55,927,881	55,677,166	55,950,467