CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income Statement [Abstract]
Service revenues	$ 1,639,478	$ 1,862,827	$ 3,355,813	$ 3,677,661
Costs of services	979,309	1,047,280	2,005,912	2,090,268
Gross margin	660,169	815,547	1,349,901	1,587,393
Selling, general and administrative expenses	541,904	509,394	1,094,133	1,023,588
(Income) loss from investments held in employee deferred compensation trusts	(28,347)	65,622	(55,638)	95,623
Amortization of intangible assets	721	416	1,442	833
Interest income, net	(5,320)	(718)	(10,145)	(884)
Income before income taxes	151,211	240,833	320,109	468,233
Provision for income taxes	44,919	65,012	91,812	124,173
Net income	$ 106,292	$ 175,821	$ 228,297	$ 344,060
Net income per share:
Basic (in usd per share)	$ 1.00	$ 1.62	$ 2.15	$ 3.16
Diluted (in usd per share)	$ 1.00	$ 1.60	$ 2.14	$ 3.12
Shares:
Basic (in shares)	106,102	108,833	106,260	109,025
Diluted (in shares)	106,422	109,696	106,775	110,143
Dividends declared per share (in usd per share)	$ 0.48	$ 0.43	$ 0.96	$ 0.86