Quarterly Financial Information (Summary Of Quarterly Financial Information) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected Quarterly Financial Information [Abstract]
Revenue	$ 592,470	$ 616,458	$ 590,304	$ 538,416	$ 533,797	$ 550,511	$ 547,452	$ 502,819	$ 2,337,648	$ 2,134,579	$ 1,903,800
Operating income	76,845	98,076	97,573	65,944	67,516	80,932	82,588	54,218	338,438	285,254	234,072
Net income	$ 47,156	$ 60,149	$ 58,255	$ 40,553	$ 39,481	$ 51,044	$ 47,832	$ 31,095	$ 206,113	$ 169,452	$ 139,470
Basic and diluted	$ 0.55	$ 0.70	$ 0.68	$ 0.47	$ 0.46	$ 0.59	$ 0.56	$ 0.36	$ 2.39	$ 1.97