Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Service revenues	$ 1,862,827	$ 1,580,581	$ 3,677,661	$ 2,978,961
Costs of services	1,047,280	915,709	2,090,268	1,752,378
Gross margin	815,547	664,872	1,587,393	1,226,583
Selling, general and administrative expenses	509,394	488,093	1,023,588	911,155
(Income) loss from investments held in employee deferred compensation trusts (which is completely offset by related costs and expenses - Notes A & I)	65,622	(27,810)	95,623	(39,797)
Amortization of intangible assets	416	576	833	1,152
Interest (income) expense, net	(718)	151	(884)	105
Income before income taxes	240,833	203,862	468,233	353,968
Provision for income taxes	65,012	54,649	124,173	94,157
Net income	$ 175,821	$ 149,213	$ 344,060	$ 259,811
Net income per share:
Basic (in usd per share)	$ 1.62	$ 1.35	$ 3.16	$ 2.34
Diluted (in usd per share)	$ 1.60	$ 1.33	$ 3.12	$ 2.32
Shares:
Basic (in shares)	108,833	110,861	109,025	111,141
Diluted (in shares)	109,696	111,889	110,143	112,191
Dividends declared per share (in usd per share)	$ 0.43	$ 0.38	$ 0.86	$ 0.76