Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
QUARTERLY INFORMATION
Revenue	$ 1,729,150	$ 1,724,418	$ 1,703,744	$ 1,629,672	$ 1,672,743	$ 1,669,066	$ 1,662,931	$ 1,567,153	$ 6,786,984	$ 6,571,893	$ 6,638,774
Earnings from Continuing Operations Before Income Taxes	69,196	131,698	116,779	88,708	111,691	139,900	133,447	84,177	406,381	469,215	338,267
Earnings from Continuing Operations	49,275	85,138	74,042	56,185	75,935	90,811	85,917	53,326	264,640	305,989	220,225
Net Earnings	$ 48,181	$ 84,752	$ 73,750	$ 55,794	$ 76,201	$ 90,619	$ 85,159	$ 52,789	$ 262,477	$ 304,768	$ 218,341
Earnings from Continuing Operations per Common Share
Earnings from continuing operations per common share — Basic (in dollars per share)	$ 0.93	$ 1.60	$ 1.39	$ 1.06	$ 1.43	$ 1.71	$ 1.62	$ 1.01	$ 4.98	$ 5.78	$ 4.18
Earnings from continuing operations per common share — Diluted (in dollars per share)	0.92	1.59	1.38	1.05	1.42	1.70	1.61	1.00	4.94	5.73	4.14
Net Earnings per Common Share
Basic (in dollars per share)	0.91	1.60	1.39	1.05	1.44	1.71	1.61	1.00	4.94	5.75	4.14
Diluted (in dollars per share)	$ 0.91	$ 1.59	$ 1.38	$ 1.04	$ 1.43	$ 1.69	$ 1.59	$ 0.99	$ 4.90	$ 5.71	$ 4.11