Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
QUARTERLY INFORMATION
Revenue	$ 1,939,693	$ 1,848,529	$ 1,793,214	$ 1,748,163	$ 1,729,150	$ 1,724,418	$ 1,703,744	$ 1,629,672	$ 7,329,599	$ 6,786,984	$ 6,571,893
Earnings from Continuing Operations Before Income Taxes	78,795	94,343	80,692	59,956	69,196	131,698	116,779	88,708	313,786	406,381	469,215
Earnings from Continuing Operations	642,480	58,913	51,343	38,279	49,275	85,138	74,042	56,185	791,015	264,640	305,989
Net Earnings	$ 642,970	$ 58,623	$ 50,816	$ 38,149	$ 48,181	$ 84,752	$ 73,750	$ 55,794	$ 790,558	$ 262,477	$ 304,768
Earnings from Continuing Operations per Common Share
Earnings from continuing operations per common share — Basic (in dollars per share)	$ 12.21	$ 1.12	$ 0.97	$ 0.72	$ 0.93	$ 1.60	$ 1.39	$ 1.06	$ 14.98	$ 4.98	$ 5.78
Earnings from continuing operations per common share — Diluted (in dollars per share)	12.10	1.11	0.97	0.71	0.92	1.59	1.38	1.05	14.87	4.94	5.73
Net Earnings per Common Share
Basic (in dollars per share)	12.22	1.11	0.96	0.72	0.91	1.60	1.39	1.05	14.97	4.94	5.75
Diluted (in dollars per share)	$ 12.11	$ 1.11	$ 0.96	$ 0.71	$ 0.91	$ 1.59	$ 1.38	$ 1.04	$ 14.87	$ 4.90	$ 5.71