Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Revenues		$ 1,690,176	$ 1,641,959	$ 1,760,303
Operating costs and expenses:
Costs of services provided		1,496,336	1,415,082	1,492,317
Selling, general and administrative expense		140,344	173,108	150,778
Other (expense) income:
Investment and other (expense) income, net		(5,427)	9,439	13,352
Interest expense		(2,987)	(1,385)	(1,374)
Income before income taxes		45,082	61,823	129,186
Income tax provision		10,452	15,960	30,504
Net income	[1]	$ 34,630	$ 45,863	$ 98,682
Per share data:
Basic earnings per common share (in dollars per share)		$ 0.47	$ 0.61	$ 1.32
Diluted earnings per common share (in dollars per share)		$ 0.47	$ 0.61	$ 1.32
Weighted average number of common shares outstanding:
Basic (in shares)		74,336	74,816	74,696
Diluted (in shares)		74,351	74,962	74,785
Comprehensive income:
Net income	[1]	$ 34,630	$ 45,863	$ 98,682
Other comprehensive income:
Unrealized (loss) gain on available-for-sale marketable securities, net of taxes		(7,477)	(1,563)	2,644
Total comprehensive income	[1]	$ 27,153	$ 44,300	$ 101,326

[1] See Note 8 — Allowance for Doubtful Accounts herein regarding the adopted credit-loss guidance.