New Accounting Pronouncements (Condensed Consolidated Statement of Income) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidated Statements Of Income (Loss) [Abstract]
Revenues	$ 608,136	$ 557,903
Cost of sales	549,818	510,371
Selling, general and administrative expenses	35,750	32,651
Amortization of Intangible Assets	2,366	2,481
Restructuring charges and other costs	2,235	1,511
Interest expense	2,428	2,225
Interest income	1,933	1,074
Other income (expense), net	43	(81)
Income tax expense	41,156	1,102
Net income (loss)	$ (23,641)	$ 8,555
Earnings Per Share [Abstract]
Basic	$ (0.49)	$ 0.17
Diluted	$ (0.49)	$ 0.17
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Basic	48,517	49,511
Diluted	48,517	50,080
Accounting Standards Update 2014-09 [Member] | As Previously Reported [Member] | Calculated Under Revenue Guidance In Effect Before Topic 606 [Member]
Condensed Consolidated Statements Of Income (Loss) [Abstract]
Revenues		$ 566,501
Cost of sales		(517,441)
Selling, general and administrative expenses		(32,651)
Amortization of Intangible Assets		(2,481)
Restructuring charges and other costs		(1,511)
Interest expense		2,225
Interest income		1,074
Other income (expense), net		(81)
Income tax expense		(1,498)
Net income (loss)		$ 9,687
Earnings Per Share [Abstract]
Basic		$ 0.2
Diluted		$ 0.19
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Basic		49,511
Diluted		50,080
Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member] | Adjustments [Member]
Condensed Consolidated Statements Of Income (Loss) [Abstract]
Revenues		$ (8,598)
Cost of sales		7,070
Selling, general and administrative expenses		0
Amortization of Intangible Assets		0
Restructuring charges and other costs		0
Interest expense		0
Interest income		0
Other income (expense), net		0
Income tax expense		396
Net income (loss)		$ (1,132)
Earnings Per Share [Abstract]
Basic		$ (0.02)
Diluted		$ (0.02)
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Basic		49,511
Diluted		50,080