Consolidated Statements of Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Statement [Abstract]
Revenues	$ 428,149	$ 411,388	$ 1,277,870	$ 1,247,549
Operating costs and expenses:
Costs of services provided	364,730	376,936	1,108,383	1,107,519
Selling, general and administrative expense	46,888	39,047	138,236	120,523
Other income (expense):
Investment and other income, net	3,825	394	12,145	7,047
Interest expense	(1,548)	(2,132)	(5,260)	(5,798)
Income (loss) before taxes	18,808	(6,333)	38,136	20,756
Income tax provision (benefit)	4,778	(1,286)	10,585	5,878
Net income (loss)	$ 14,030	$ (5,047)	$ 27,551	$ 14,878
Per share data:
Basic (loss) per common share (in dollars per share)	$ 0.19	$ (0.07)	$ 0.37	$ 0.20
Diluted (loss) per common share (in dollars per share)	$ 0.19	$ (0.07)	$ 0.37	$ 0.20
Weighted average number of common shares outstanding:
Basic (in shares)	73,687	74,364	73,822	74,446
Diluted (in shares)	73,926	74,364	74,007	74,496
Comprehensive income (loss):
Net income (loss)	$ 14,030	$ (5,047)	$ 27,551	$ 14,878
Other comprehensive income (loss)
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	2,093	(1,647)	1,320	(1,300)
Total comprehensive income (loss)	$ 16,123	$ (6,694)	$ 28,871	$ 13,578