Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
Revenues	$ 423,433	$ 417,230
Operating costs and expenses:
Costs of services provided	358,911	362,379
Selling, general and administrative expense	46,911	40,047
Other income (expense):
Investment and other income, net	5,699	3,102
Interest expense	(1,996)	(1,751)
Income before income taxes	21,314	16,155
Income tax provision	6,005	4,484
Net income	$ 15,309	$ 11,671
Per share data:
Basic earnings per common share (in dollars per share)	$ 0.21	$ 0.16
Diluted earnings per common share (in dollars per share)	$ 0.21	$ 0.16
Weighted average number of common shares outstanding:
Basic (in shares)	73,926	74,497
Diluted (in shares)	74,055	74,518
Comprehensive income:
Net income	$ 15,309	$ 11,671
Other comprehensive income:
Unrealized (loss) gain on available-for-sale marketable securities, net of taxes	(328)	1,207
Total comprehensive income	$ 14,981	$ 12,878