CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
REVENUES
Customer services	$ 3,073,278	$ 2,695,823	$ 2,424,300
Revenue from Contract with Customer, Product and Service [Extensible Enumeration]	Customer Services [Member]	Customer Services [Member]	Customer Services [Member]
COSTS AND EXPENSES
Cost of services provided (exclusive of depreciation and amortization below)	$ 1,469,871	$ 1,308,399	$ 1,162,617
Sales, general and administrative	915,233	802,710	727,489
Restructuring costs	5,196	0	0
Depreciation and amortization	99,752	91,326	86,558
Total operating expenses	2,490,052	2,202,435	1,976,664
OPERATING INCOME	583,226	493,388	447,636
Interest expense, net	19,055	2,638	830
Other (income), net	(22,086)	(8,167)	(35,679)
CONSOLIDATED INCOME BEFORE INCOME TAXES	586,257	498,917	482,485
PROVISION FOR INCOME TAXES	151,300	130,318	125,920
NET INCOME	$ 434,957	$ 368,599	$ 356,565
NET INCOME PER SHARE - BASIC (in USD per share)	$ 0.89	$ 0.75	$ 0.72
NET INCOME PER SHARE - DILUTED (in USD per share)	$ 0.89	$ 0.75	$ 0.72
Weighted average shares outstanding - basic (in shares)	489,949	492,300	492,054
Weighted average shares outstanding - diluted (in shares)	490,130	492,413	492,054
DIVIDENDS PAID PER SHARE (in USD per share)	$ 0.54	$ 0.43	$ 0.42