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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Data [Line Items]
Revenues	$ 1,363,877	$ 1,404,113	$ 1,446,096	$ 1,366,161	$ 1,318,698	$ 1,377,079	$ 1,348,549	$ 1,245,627	$ 5,580,247	$ 5,289,953	$ 4,952,000
Operating Income	37,795	55,213	80,143	55,690	49,942	61,125	60,165	36,696	228,841	207,928	78,170
Income (Loss) from before Income Tax Provision (Benefit)	23,677	41,158	64,697	41,422	33,661	47,606	45,444	21,361	170,954	148,072	16,557
Income Tax Provision (Benefit)	11,881	15,854	22,897	15,776	10,690	18,478	16,022	14,439	66,408	59,629	12,572
Net Income (Loss) Applicable to Common Shareholders	$ 11,796	$ 25,304	$ 41,800	$ 25,646	$ 22,971	$ 29,128	$ 29,422	$ 6,922
Basic Earnings	$ 0.21	$ 0.45	$ 0.75	$ 0.46	$ 0.41	$ 0.52	$ 0.53	$ 0.13	$ 1.87	$ 1.60	$ 0.08
Diluted Earnings per Share	$ 0.21	$ 0.45	$ 0.74	$ 0.46	$ 0.41	$ 0.52	$ 0.52	$ 0.12	$ 1.85	$ 1.58	$ 0.07
Cash Dividends	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10
Minimum [Member]
Quarterly Financial Data [Line Items]
Market price	25.97	26.51	30.89	28.26	20.56	21.32	35.42	30.56
Maximum [Member]
Quarterly Financial Data [Line Items]
Market price	29.91	37.30	38.78	34.69	30.71	42.38	40.36	39.78