Summary Of Significant Accounting Policies (Condensed Consolidated Statement of Income) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Consolidated Statements Of Income (Loss) [Abstract]
Revenues	$ 657,050	$ 640,688	$ 660,591	$ 608,136	$ 666,036	$ 610,929	$ 619,611	$ 557,903	$ 620,043	$ 586,534	$ 580,513	$ 535,195	$ 2,566,465	$ 2,454,479	$ 2,322,285
Cost of sales													2,345,872	2,228,559	2,107,600
Income tax expense													32,724	102,906	5,477
Net income (loss)	$ 27,716	$ 7,799	$ 10,943	$ (23,641)	$ (76,361)	$ 17,831	$ 18,074	$ 8,555	$ 19,327	$ 22,544	$ 12,688	$ 9,374	$ 22,817	$ (31,901)	$ 63,933
Earnings Per Share [Abstract]
Basic	$ 0.64	$ 0.17	$ 0.23	$ (0.49)	$ (1.54)	$ 0.36	$ 0.36	$ 0.17	$ 0.39	$ 0.46	$ 0.26	$ 0.19	$ 0.49	$ (0.64)	$ 1.3
Diluted	$ 0.64	$ 0.17	$ 0.23	$ (0.49)	$ (1.54)	$ 0.35	$ 0.36	$ 0.17	$ 0.39	$ 0.46	$ 0.26	$ 0.19	$ 0.49	$ (0.64)	$ 1.28
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Basic													46,332	49,680	49,298
Diluted													46,655	49,680	49,825
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														$ 2,466,811	$ 2,310,415
Cost of sales														2,239,114	2,096,952
Income tax expense														104,747	4,141
Net income (loss)														$ (31,965)	$ 64,047
Earnings Per Share [Abstract]
Basic														$ (0.64)	$ 1.3
Diluted														$ (0.64)	$ 1.29
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Basic														49,680	49,298
Diluted														49,680	49,825
Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member] | Adjustments [Member]
Condensed Consolidated Statements Of Income (Loss) [Abstract]
Revenues														$ (12,332)	$ 11,870
Cost of sales														(10,555)	10,648
Income tax expense														(1,841)	1,336
Net income (loss)														$ 64	$ (114)
Earnings Per Share [Abstract]
Basic														$ 0	$ 0
Diluted														$ 0	$ (0.01)
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Basic														49,680	49,298
Diluted														49,680	49,825