Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Statement [Abstract]
Revenues	$ 417,230	$ 426,811
Operating costs and expenses:
Costs of services provided	360,978	373,262
Selling, general and administrative expense	40,047	35,736
Other income (expense):
Investment and other income (loss), net	3,102	(1,523)
Interest expense	(1,751)	(509)
Income before income taxes	17,556	15,781
Income tax provision	4,872	4,452
Net income	$ 12,684	$ 11,329
Per share data:
Basic earnings per common share (in dollars per share)	$ 0.17	$ 0.15
Diluted earnings per common share (in dollars per share)	$ 0.17	$ 0.15
Weighted average number of common shares outstanding:
Basic (in shares)	74,497	74,326
Diluted (in shares)	74,518	74,333
Comprehensive income:
Net income	$ 12,684	$ 11,329
Other comprehensive gain (loss):
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	1,207	(5,269)
Total comprehensive income	$ 13,891	$ 6,060