Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Revenues	$ 426,811	$ 407,751
Operating costs and expenses:
Costs of services provided	373,262	336,619
Selling, general and administrative expense	35,736	39,987
Other (expense) income:
Investment and other (loss) income, net	(1,523)	2,165
Interest expense	(509)	(358)
Income before income taxes	15,781	32,952
Income tax provision	4,452	8,299
Net income	$ 11,329	$ 24,653
Per share data:
Basic earnings per share (in dollars per share)	$ 0.15	$ 0.33
Diluted earnings per share (in dollars per share)	$ 0.15	$ 0.33
Weighted average number of common shares outstanding:
Basic (in shares)	74,326	75,003
Diluted (in shares)	74,333	75,224
Comprehensive income:
Net income	$ 11,329	$ 24,653
Other comprehensive loss:
Unrealized loss on available-for-sale marketable securities, net of taxes	(5,269)	(1,271)
Total comprehensive income	$ 6,060	$ 23,382