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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
REVENUE	$ 568,430	$ 574,448	$ 571,891	$ 565,490	$ 562,938	$ 568,197	$ 552,319	$ 535,140	$ 2,280,259	$ 2,218,594	$ 2,120,972
COST OF SERVICES	239,389	246,337	245,266	239,701	234,419	243,706	239,695	225,511	970,693	943,331	894,628
Gross profit	329,041	328,111	326,625	325,789	328,519	324,491	312,624	309,629	1,309,566	1,275,263
SG&A	224,071	203,757	210,192	215,096	211,809	209,545	197,063	195,439	853,116	813,856	775,050
OPERATING INCOME	104,970	124,354	116,433	110,693	116,710	114,946	115,561	114,190	456,450	461,407	451,294
Income from continuing operations	42,340	50,719	49,223	48,634	34,884	13,103	44,527	42,097	190,916	134,611	123,091
Income (loss) from discontinued operations	19,935	(1,235)	358	31,866	13,374	3,007	3,232	4,181	50,924	23,794	20,111
Net income	$ 62,275	$ 49,484	$ 49,581	$ 80,500	$ 48,258	$ 16,110	$ 47,759	$ 46,278	$ 241,840	$ 158,405	$ 143,202
EARNINGS PER COMMON SHARE - DILUTED
Continuing Operations	$ 0.50	$ 0.60	$ 0.58	$ 0.56	$ 0.41	$ 0.15	$ 0.52	$ 0.49	$ 2.24	$ 1.57	$ 1.53
Discontinued Operations	0.24	$ (0.01)	0.00	0.37	0.15	0.04	0.04	0.05	0.59	0.28	0.25
Diluted earnings per common share:	$ 0.74		$ 0.58	$ 0.93	$ 0.56	$ 0.19	$ 0.56	$ 0.54	$ 2.83	$ 1.85	$ 1.78