Quarterly Results of Operations (Unaudited) - Unaudited Quarterly Results of Operations (Detail) - 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 Financial Information Disclosure [Abstract]
REVENUE	$ 567,380	$ 571,407	$ 582,397	$ 570,779	$ 568,430	$ 574,448	$ 571,891	$ 565,490	$ 2,291,963	$ 2,280,259	$ 2,218,594
COST OF SERVICES	243,533	247,817	249,426	241,012	239,389	246,337	245,266	239,701	981,788	970,693	943,331
Gross profit	323,847	323,590	332,971	329,767	329,041	328,111	326,625	325,789	1,310,175	1,309,566
SG&A	221,157	214,091	209,870	220,843	224,071	203,757	210,192	215,096	865,961	853,116	813,856
OPERATING INCOME	102,690	109,499	123,101	108,924	104,970	124,354	116,433	110,693	444,214	456,450	461,407
Income from continuing operations					42,340	50,719	49,223	48,634	193,389	190,916	134,611
Income (loss) from discontinued operations					19,935	(1,235)	358	31,866	0	50,924	23,794
Net income	$ 68,320	$ 47,535	$ 32,979	$ 44,555	$ 62,275	$ 49,484	$ 49,581	$ 80,500	$ 193,389	$ 241,840	$ 158,405
EARNINGS PER COMMON SHARE—DILUTED
Continuing Operations					$ 0.50	$ 0.60	$ 0.58	$ 0.56	$ 2.29	$ 2.24	$ 1.57
Discontinued Operations					0.24	(0.01)	0.00	0.37	0	0.59	0.28
Diluted earnings per common share:	$ 0.80	$ 0.56	$ 0.39	$ 0.53	$ 0.74	$ 0.58	$ 0.58	$ 0.93	$ 2.29	$ 2.83	$ 1.85