Segment Information (Schedule Of Revenue And Long-Lived Assets, By Geographical Areas) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	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, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 567,365	$ 528,643	$ 519,508	$ 501,221	$ 518,832	$ 508,676	$ 498,681	$ 482,802	$ 2,116,737	$ 2,008,991	$ 2,093,529
Long-lived assets	1,346,863				1,362,638				1,346,863	1,362,638	1,154,470
United States [Member]
Segment Reporting Information [Line Items]
Revenues									1,837,525	1,760,214	1,821,026
Long-lived assets	1,321,206				1,341,703				1,321,206	1,341,703	1,134,433
Mexico [Member]
Segment Reporting Information [Line Items]
Revenues									210,228	183,058	191,453
Long-lived assets	25,309				20,614				25,309	20,614	19,879
Other [Member]
Segment Reporting Information [Line Items]
Revenues									68,984	65,719	81,050
Long-lived assets	348				321				348	321	158
Total Foreign Countries [Member]
Segment Reporting Information [Line Items]
Revenues									279,212	248,777	272,503
Long-lived assets	$ 25,657				$ 20,935				$ 25,657	$ 20,935	$ 20,037