Quarterly Information (Unaudited) (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 INFORMATION
Revenue	$ 1,656,316	$ 1,687,150	$ 1,684,571	$ 1,610,737	$ 1,617,729	$ 1,634,540	$ 1,603,999	$ 1,563,017	$ 6,638,774	$ 6,419,285	$ 6,256,967
Earnings from Continuing Operations	11,700	83,967	75,694	49,098	65,944	73,875	62,575	40,802	220,459	243,196	200,899
Net Earnings	$ 11,296	$ 83,689	$ 75,358	$ 48,232	$ 64,607	$ 71,067	$ 62,194	$ 39,924	$ 218,575	$ 237,792	$ 209,979
Earnings from Continuing Operations per Common Share
Earnings from continuing operations per common share — Basic	$ 0.22	$ 1.60	$ 1.43	$ 0.93	$ 1.25	$ 1.41	$ 1.21	$ 0.79	$ 4.18	$ 4.67	$ 3.93
Earnings from continuing operations per common share — Diluted	$ 0.22	$ 1.58	$ 1.42	$ 0.92	$ 1.24	$ 1.40	$ 1.19	$ 0.79	$ 4.14	$ 4.63	$ 3.91
Net Earnings per Common Share
Basic (USD per share)	$ 0.21	$ 1.59	$ 1.43	$ 0.91	$ 1.23	$ 1.36	$ 1.20	$ 0.77	$ 4.14	$ 4.57	$ 4.11
Diluted (USD per share)	$ 0.21	$ 1.57	$ 1.41	$ 0.90	$ 1.22	$ 1.35	$ 1.19	$ 0.77	$ 4.11	$ 4.53	$ 4.09