Quarterly Financial Data (Components Of Quarterly Financial Data) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Line Items]
Revenue	$ 1,440,727	$ 1,504,150	$ 1,492,349	$ 1,368,843	$ 1,357,801	$ 1,398,021	$ 1,381,370	$ 1,336,164	$ 5,806,069	$ 5,473,356	$ 5,580,247
Operating Income	41,313	91,375	102,700	33,062	33,380	67,675	76,299	31,599	268,450	208,953	228,841
Income before Income Tax Provision (Benefit)	23,317	77,390	90,768	19,222	21,363	53,378	62,849	16,775	210,697	154,365	170,954
Income Tax Provision (Benefit)	(1,579)	31,807	37,101	6,329	9,669	22,821	19,952	2,770	73,658	55,212	66,408
Net Income	$ 24,896	$ 45,583	$ 53,667	$ 12,893	$ 11,694	$ 30,557	$ 42,897	$ 14,005
Earnings Per Common Share, Basic	$ 0.43	$ 0.79	$ 0.94	$ 0.23	$ 0.21	$ 0.54	$ 0.76	$ 0.25	$ 2.39	$ 1.75	$ 1.87
Earnings per common share, diluted	$ 0.43	$ 0.78	$ 0.93	$ 0.22	$ 0.20	$ 0.53	$ 0.75	$ 0.25	$ 2.36	$ 1.73	$ 1.85
Cash Dividends Paid per Common Share	$ 0.15	$ 0.15	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10
Minimum [Member]
Quarterly Financial Data [Line Items]
Market Price per Common Share	40.32	47.50	39.54	37.00	38.79	39.21	32.25	29.12
Maximum [Member]
Quarterly Financial Data [Line Items]
Market Price per Common Share	50.81	53.53	50.46	42.73	45.98	46.04	39.81	38.12