Revenue Recognition - Disaggregated Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Disaggregation of Revenue [Line Items]
Revenues	$ 952,972	$ 866,286	$ 2,714,814	$ 2,312,583
Fixed-Price Incentive Fee
Disaggregation of Revenue [Line Items]
Revenues	484,662	240,406	852,376	677,457
Firm-Fixed-Price
Disaggregation of Revenue [Line Items]
Revenues	204,167	427,878	1,181,430	1,153,197
Cost-Plus Fee
Disaggregation of Revenue [Line Items]
Revenues	153,324	98,865	363,319	298,608
Time-and-Materials
Disaggregation of Revenue [Line Items]
Revenues	111,125	100,519	321,501	187,101
Over time
Disaggregation of Revenue [Line Items]
Revenues	892,063	833,527	2,577,085	2,226,823
Point-in-time
Disaggregation of Revenue [Line Items]
Revenues	61,215	34,141	141,541	89,540
Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	953,278	867,668	2,718,626	2,316,363
Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	639,076	616,697	1,818,266	1,760,943
Operating Segments \| Government Operations \| Fixed-Price Incentive Fee
Disaggregation of Revenue [Line Items]
Revenues	483,620	239,901	850,567	669,107
Operating Segments \| Government Operations \| Firm-Fixed-Price
Disaggregation of Revenue [Line Items]
Revenues	11,465	279,993	623,931	795,008
Operating Segments \| Government Operations \| Cost-Plus Fee
Disaggregation of Revenue [Line Items]
Revenues	143,497	96,706	342,746	296,602
Operating Segments \| Government Operations \| Time-and-Materials
Disaggregation of Revenue [Line Items]
Revenues	494	97	1,022	226
Operating Segments \| Government Operations \| Over time
Disaggregation of Revenue [Line Items]
Revenues	631,375	612,212	1,797,004	1,749,201
Operating Segments \| Government Operations \| Point-in-time
Disaggregation of Revenue [Line Items]
Revenues	7,701	4,485	21,262	11,742
Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	314,202	250,971	900,360	555,420
Operating Segments \| Commercial Operations \| Fixed-Price Incentive Fee
Disaggregation of Revenue [Line Items]
Revenues	1,042	505	1,809	8,350
Operating Segments \| Commercial Operations \| Firm-Fixed-Price
Disaggregation of Revenue [Line Items]
Revenues	192,702	147,885	557,499	358,189
Operating Segments \| Commercial Operations \| Cost-Plus Fee
Disaggregation of Revenue [Line Items]
Revenues	9,827	2,159	20,573	2,006
Operating Segments \| Commercial Operations \| Time-and-Materials
Disaggregation of Revenue [Line Items]
Revenues	110,631	100,422	320,479	186,875
Operating Segments \| Commercial Operations \| Over time
Disaggregation of Revenue [Line Items]
Revenues	260,688	221,315	780,081	477,622
Operating Segments \| Commercial Operations \| Point-in-time
Disaggregation of Revenue [Line Items]
Revenues	53,514	29,656	120,279	77,798
Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(306)	(1,382)	(3,812)	(3,780)
United States
Disaggregation of Revenue [Line Items]
Revenues	693,169	643,681	1,928,535	1,817,784
United States \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	620,872	610,537	1,768,326	1,743,727
United States \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	72,297	33,144	160,209	74,057
Canada
Disaggregation of Revenue [Line Items]
Revenues	227,204	199,545	689,010	442,558
Canada \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	8,534	191	26,568	425
Canada \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	218,670	199,354	662,442	442,133
Other
Disaggregation of Revenue [Line Items]
Revenues	32,905	24,442	101,081	56,021
Other \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	9,670	5,969	23,372	16,791
Other \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	23,235	18,473	77,709	39,230
Government \| United States
Disaggregation of Revenue [Line Items]
Revenues	623,419	572,401	1,718,563	1,611,629
Government \| United States \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	596,938	572,313	1,691,241	1,611,357
Government \| United States \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	26,481	88	27,322	272
Government \| Canada
Disaggregation of Revenue [Line Items]
Revenues	8,292	159	26,088	271
Government \| Canada \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	8,292	159	26,088	271
Government \| Canada \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Government \| Other
Disaggregation of Revenue [Line Items]
Revenues	6,147	3,701	12,196	11,297
Government \| Other \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	6,125	3,701	12,174	11,297
Government \| Other \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	22	0	22	0
Non-Government \| United States
Disaggregation of Revenue [Line Items]
Revenues	69,750	71,280	209,972	206,155
Non-Government \| United States \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	23,934	38,224	77,085	132,370
Non-Government \| United States \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	45,816	33,056	132,887	73,785
Non-Government \| Canada
Disaggregation of Revenue [Line Items]
Revenues	218,912	199,386	662,922	442,287
Non-Government \| Canada \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	242	32	480	154
Non-Government \| Canada \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	218,670	199,354	662,442	442,133
Non-Government \| Other
Disaggregation of Revenue [Line Items]
Revenues	26,758	20,741	88,885	44,724
Non-Government \| Other \| Operating Segments \| Government Operations
Disaggregation of Revenue [Line Items]
Revenues	3,545	2,268	11,198	5,494
Non-Government \| Other \| Operating Segments \| Commercial Operations
Disaggregation of Revenue [Line Items]
Revenues	$ 23,213	$ 18,473	$ 77,687	$ 39,230