CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Statement [Abstract]
Service revenues	$ 1,465,004	$ 1,563,812	$ 4,413,465	$ 4,919,625
Costs of services	893,348	922,873	2,702,333	2,928,785
Gross margin	571,656	640,939	1,711,132	1,990,840
Selling, general and administrative expenses	510,786	496,732	1,533,213	1,590,865
(Income) loss from investments held in employee deferred compensation trusts (which is completely offset by related costs and expenses - Note A)	(29,230)	14,275	(88,339)	(41,363)
Amortization of intangible assets	305	720	913	2,162
Interest income, net	(5,391)	(7,131)	(16,990)	(17,276)
Income before income taxes	95,186	136,343	282,335	456,452
Provision for income taxes	29,735	40,798	85,027	132,610
Net income	$ 65,451	$ 95,545	$ 197,308	$ 323,842
Net income per share:
Basic (in usd per share)	$ 0.64	$ 0.91	$ 1.91	$ 3.06
Diluted (in usd per share)	$ 0.64	$ 0.90	$ 1.91	$ 3.04
Weighted average shares:
Basic (in shares)	102,175	105,340	103,034	105,950
Diluted (in shares)	102,393	105,810	103,371	106,450
Dividends declared per share (in usd per share)	$ 0.53	$ 0.48	$ 1.59	$ 1.44