Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenues	$ 885,842	$ 866,286	$ 764,039	$ 682,258	$ 746,267	$ 671,956	$ 681,465	$ 603,966	$ 3,198,425	$ 2,703,654	$ 2,496,309
Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									3,203,160	2,707,012	2,497,681
Eliminations
Disaggregation of Revenue [Line Items]
Revenues									(4,735)	(3,358)	(1,372)
Fixed-Price Incentive Fee
Disaggregation of Revenue [Line Items]
Revenues									904,700	1,191,107	1,229,635
Firm-Fixed-Price
Disaggregation of Revenue [Line Items]
Revenues									1,582,046	905,945	781,374
Cost-Plus Fee
Disaggregation of Revenue [Line Items]
Revenues									420,518	388,116	337,598
Time-and-Materials
Disaggregation of Revenue [Line Items]
Revenues									295,896	221,844	149,074
Over time
Disaggregation of Revenue [Line Items]
Revenues									3,058,113	2,614,514	2,405,009
Point-in-time
Disaggregation of Revenue [Line Items]
Revenues									145,047	92,498	92,672
United States:
Disaggregation of Revenue [Line Items]
Revenues									2,431,324	2,230,205	2,065,929
United States: \| Government
Disaggregation of Revenue [Line Items]
Revenues									2,199,998	2,068,239	1,884,671
United States: \| Non-Government
Disaggregation of Revenue [Line Items]
Revenues									231,326	161,966	181,258
Canada:
Disaggregation of Revenue [Line Items]
Revenues									688,609	431,259	390,257
Canada: \| Government
Disaggregation of Revenue [Line Items]
Revenues									3,619	127	245
Canada: \| Non-Government
Disaggregation of Revenue [Line Items]
Revenues									684,990	431,132	390,012
Other:
Disaggregation of Revenue [Line Items]
Revenues									83,227	45,548	41,495
Other: \| Government
Disaggregation of Revenue [Line Items]
Revenues									15,731	12,165	10,016
Other: \| Non-Government
Disaggregation of Revenue [Line Items]
Revenues									67,496	33,383	31,479
Government Operations \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									2,350,090	2,183,040	2,031,337
Government Operations \| Fixed-Price Incentive Fee
Disaggregation of Revenue [Line Items]
Revenues									894,366	1,173,728	1,218,516
Government Operations \| Firm-Fixed-Price
Disaggregation of Revenue [Line Items]
Revenues									1,042,344	590,884	469,138
Government Operations \| Cost-Plus Fee
Disaggregation of Revenue [Line Items]
Revenues									412,701	388,116	337,598
Government Operations \| Time-and-Materials
Disaggregation of Revenue [Line Items]
Revenues									679	30,312	6,085
Government Operations \| Over time
Disaggregation of Revenue [Line Items]
Revenues									2,337,024	2,175,010	2,012,949
Government Operations \| Point-in-time
Disaggregation of Revenue [Line Items]
Revenues									13,066	8,030	18,388
Government Operations \| United States: \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									2,323,608	2,154,251	2,008,275
Government Operations \| United States: \| Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									2,199,677	2,068,239	1,884,671
Government Operations \| United States: \| Non-Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									123,931	86,012	123,604
Government Operations \| Canada: \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									3,745	874	1,023
Government Operations \| Canada: \| Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									3,619	127	245
Government Operations \| Canada: \| Non-Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									126	747	778
Government Operations \| Other: \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									22,737	27,915	22,039
Government Operations \| Other: \| Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									15,731	12,165	10,016
Government Operations \| Other: \| Non-Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									7,006	15,750	12,023
Commercial Operations \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									853,070	523,972	466,344
Commercial Operations \| Fixed-Price Incentive Fee
Disaggregation of Revenue [Line Items]
Revenues									10,334	17,379	11,119
Commercial Operations \| Firm-Fixed-Price
Disaggregation of Revenue [Line Items]
Revenues									539,702	315,061	312,236
Commercial Operations \| Cost-Plus Fee
Disaggregation of Revenue [Line Items]
Revenues									7,817	0	0
Commercial Operations \| Time-and-Materials
Disaggregation of Revenue [Line Items]
Revenues									295,217	191,532	142,989
Commercial Operations \| Over time
Disaggregation of Revenue [Line Items]
Revenues									721,089	439,504	392,060
Commercial Operations \| Point-in-time
Disaggregation of Revenue [Line Items]
Revenues									131,981	84,468	74,284
Commercial Operations \| United States: \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									107,716	75,954	57,654
Commercial Operations \| United States: \| Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									321	0	0
Commercial Operations \| United States: \| Non-Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									107,395	75,954	57,654
Commercial Operations \| Canada: \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									684,864	430,385	389,234
Commercial Operations \| Canada: \| Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Commercial Operations \| Canada: \| Non-Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									684,864	430,385	389,234
Commercial Operations \| Other: \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									60,490	17,633	19,456
Commercial Operations \| Other: \| Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									0	0	0
Commercial Operations \| Other: \| Non-Government \| Reportable Segments
Disaggregation of Revenue [Line Items]
Revenues									$ 60,490	$ 17,633	$ 19,456