Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Consolidated Statements Of Income (Loss) [Abstract]
Net sales	$ 660,591	$ 619,611	$ 1,268,727	$ 1,177,514
Cost of sales	606,292	560,127	1,156,110	1,070,498
Gross profit	54,299	59,484	112,617	107,016
Selling, general and administrative expenses	35,825	32,335	71,575	64,986
Amortization of intangible assets	2,367	2,481	4,733	4,962
Restructuring charges and other costs	1,758	1,544	3,993	3,055
Income from operations	14,349	23,124	32,316	34,013
Interest expense	(2,293)	(2,312)	(4,721)	(4,537)
Interest income	1,645	1,213	3,578	2,287
Other expense	(355)	(830)	(312)	(911)
Income before income taxes	13,346	21,195	30,861	30,852
Income tax expense	2,403	3,121	43,559	4,223
Net income (loss)	$ 10,943	$ 18,074	$ (12,698)	$ 26,629
Earnings (loss) per share:
Basic	$ 0.23	$ 0.36	$ (0.26)	$ 0.54
Diluted	$ 0.23	$ 0.36	$ (0.26)	$ 0.53
Weighted-average number of shares outstanding:
Basic	47,451	49,766	47,981	49,640
Diluted	47,631	50,239	47,981	50,209