Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Service revenues	$ 7,238,142	$ 6,461,444	$ 5,109,000
Costs of services	4,144,093	3,765,416	3,096,389
Gross margin	3,094,049	2,696,028	2,012,611
Selling, general and administrative expenses	2,117,296	1,951,282	1,666,041
(Income) loss from investments held in employee deferred compensation trusts	86,139	(61,078)	(75,188)
Amortization of intangible assets	1,667	2,241	1,219
Interest income, net	(8,008)	(197)	(1,343)
Income before income taxes	896,955	803,780	421,882
Provision for income taxes	239,036	205,154	115,606
Net income	$ 657,919	$ 598,626	$ 306,276
Net income per share:
Basic (usd per share)	$ 6.08	$ 5.42	$ 2.72
Diluted (usd per share)	$ 6.03	$ 5.36	$ 2.70
Shares:
Basic (in shares)	108,214	110,482	112,729
Diluted (in shares)	109,171	111,718	113,318
Dividends declared per share (usd per share)	$ 1.72	$ 1.52	$ 1.36