Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Income Statement [Abstract]
Revenues	$ 464,338	$ 428,149	$ 1,370,491	$ 1,277,870
Operating costs and expenses:
Costs of services provided	367,933	364,730	1,203,157	1,108,383
Selling, general and administrative expense	50,541	46,888	144,670	138,236
Other income (expense):
Investment and other income, net	11,837	3,825	17,856	12,145
Interest expense	(393)	(1,548)	(1,206)	(5,260)
Income before taxes	57,308	18,808	39,314	38,136
Income tax provision	14,355	4,778	11,499	10,585
Net income	$ 42,953	$ 14,030	$ 27,815	$ 27,551
Per share data:
Basic income per common share (in dollars per share)	$ 0.59	$ 0.19	$ 0.38	$ 0.37
Diluted income per common share (in dollars per share)	$ 0.59	$ 0.19	$ 0.38	$ 0.37
Weighted average number of common shares outstanding:
Basic (in shares)	72,237	73,687	73,019	73,822
Diluted (in shares)	72,966	73,926	73,505	74,007
Comprehensive income:
Net income	$ 42,953	$ 14,030	$ 27,815	$ 27,551
Other comprehensive income
Unrealized gain on available-for-sale marketable securities, net of taxes	713	2,093	1,588	1,320
Total comprehensive income	$ 43,666	$ 16,123	$ 29,403	$ 28,871