Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Service revenues	$ 1,398,380	$ 1,506,691
Costs of services	836,669	892,303
Gross margin	561,711	614,388
Selling, general and administrative expenses	423,062	442,868
(Income) loss from investments held in employee deferred compensation trusts (which is completely offset by related costs and expenses - Notes A & I)	(11,988)	40,376
Amortization of intangible assets	576	338
Interest income, net	(45)	(957)
Income before income taxes	150,106	131,763
Provision for income taxes	39,508	41,848
Net income	$ 110,598	$ 89,915
Net income per share:
Basic (in usd per share)	$ 0.99	$ 0.79
Diluted (in usd per share)	$ 0.98	$ 0.79
Shares:
Basic (in shares)	111,424	113,187
Diluted (in shares)	112,496	113,858
Dividends declared per share (in usd per share)	$ 0.38	$ 0.34