Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Revenues	$ 424,857	$ 398,171	$ 851,668	$ 805,922
Operating costs and expenses:
Costs of services provided	379,370	336,411	752,632	673,030
Selling, general and administrative expense	29,281	50,051	65,017	90,038
Other (expense) income:
Investment and other (loss) income, net	(7,511)	3,684	(9,034)	5,849
Interest expense	(445)	(330)	(954)	(688)
Income before income taxes	8,250	15,063	24,031	48,015
Income tax provision	1,430	5,498	5,882	13,797
Net income	$ 6,820	$ 9,565	$ 18,149	$ 34,218
Per share data:
Basic earnings per share (in dollars per share)	$ 0.09	$ 0.13	$ 0.24	$ 0.46
Diluted earnings per share (in dollars per share)	$ 0.09	$ 0.13	$ 0.24	$ 0.45
Weighted average number of common shares outstanding:
Basic (in shares)	74,337	75,005	74,332	75,004
Diluted (in shares)	74,358	75,212	74,345	75,218
Comprehensive income:
Net income	$ 6,820	$ 9,565	$ 18,149	$ 34,218
Other comprehensive loss:
Unrealized (loss) gain on available-for-sale marketable securities, net of taxes	(1,945)	703	(7,214)	(568)
Total comprehensive income	$ 4,875	$ 10,268	$ 10,935	$ 33,650