Segment Information - Components of Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Components of Segment Information
Revenues	$ 358,178	$ 285,370	$ 1,022,832	$ 818,744
Operating income	37,342	29,299	95,492	74,261
Reimbursable expenses	9,288	6,816	25,918	19,034
Total revenues and reimbursable expenses	367,466	292,186	1,048,750	837,778
Restructuring charges	5,402	1,332	9,385	4,956
Depreciation and amortization	6,104	6,812	18,621	20,578
Total other income (expense), net	(6,047)	(3,896)	(13,365)	10,946
Income (loss) from continuing operations before income taxes	31,295	25,403	82,127	85,207
Healthcare
Components of Segment Information
Revenues	179,177	131,319	501,994	381,669
Education
Components of Segment Information
Revenues	111,043	94,347	325,884	263,234
Commercial:
Components of Segment Information
Revenues	67,958	59,704	194,954	173,841
Operating segments
Components of Segment Information
Revenues	358,178	285,370	1,022,832	818,744
Operating income	88,870	70,049	245,377	188,571
Reimbursable expenses	9,288	6,816	25,918	19,034
Total revenues and reimbursable expenses	367,466	292,186	1,048,750	837,778
Operating segments | Healthcare
Components of Segment Information
Revenues	179,177	131,319	501,994	381,669
Operating income	$ 46,888	$ 33,045	$ 128,294	$ 91,441
Segment operating income as a percentage of segment revenues	26.20%	25.20%	25.60%	24.00%
Operating segments | Education
Components of Segment Information
Revenues	$ 111,043	$ 94,347	$ 325,884	$ 263,234
Operating income	$ 26,550	$ 22,851	$ 77,112	$ 58,848
Segment operating income as a percentage of segment revenues	23.90%	24.20%	23.70%	22.40%
Operating segments | Commercial:
Components of Segment Information
Revenues	$ 67,958	$ 59,704	$ 194,954	$ 173,841
Operating income	$ 15,432	$ 14,153	$ 39,971	$ 38,282
Segment operating income as a percentage of segment revenues	22.70%	23.70%	20.50%	22.00%
Segment reconciling items
Components of Segment Information
Operating income	$ 37,342	$ 29,299	$ 95,492	$ 74,261
Other operating expenses	43,086	34,875	129,563	96,376
Restructuring charges	4,095	804	6,881	2,763
Depreciation and amortization	4,347	5,071	13,441	15,171
Total other income (expense), net	$ (6,047)	$ (3,896)	$ (13,365)	$ 10,946