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Reportable Segments - Financial Information (Details) - USD ($) $ in Thousands |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2025 | Sep. 28, 2025 | Jun. 29, 2025 | Mar. 30, 2025 | Dec. 29, 2024 | Sep. 29, 2024 | Jun. 30, 2024 | Mar. 31, 2024 | Dec. 31, 2023 | Sep. 28, 2025 | Sep. 29, 2024 | Oct. 01, 2023
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  | $ 1,330,100 | $ 1,369,816 | $ 1,322,113 | $ 1,420,561 | $ 1,374,473 | $ 1,344,323 | $ 1,251,616 | $ 1,228,267 | $ 5,442,590 | $ 5,198,679 | $ 4,522,550
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 825,230 | 876,817 | 771,461
Other segment items |  |  |  |  |  |  |  |  |  | (3,919,944) | (3,712,326) | (3,275,577)
Segment operating income |  | $ 181,304 | $ 164,986 | $ 39,603 | 22,526 | $ 143,343 | $ 128,630 | $ 117,683 | $ 111,081 | 408,419 | 500,737 | 358,113
Reconciliation of profit (segment operating income): |  |  |  |  |  |  |  |  |  |  |  |
Legal contingency costs |  |  |  |  | $ (115,000) |  |  |  |  | (115,000) | 0 | 0
Acquisition and integration expenses |  |  |  |  |  |  |  |  |  |  | (7,138) | (28,105)
Right-of-use operating lease asset impairment |  |  |  |  |  |  |  |  |  | 0 | 0 | (16,385)
Impairment of goodwill | $ 0 |  |  |  |  |  |  |  |  | (92,416) | 0 | 0
Contingent consideration – fair value adjustments |  |  |  |  |  |  |  |  |  | 12,228 | (2,541) | (12,255)
Interest income |  |  |  |  |  |  |  |  |  | 9,837 | 7,288 | 5,898
Interest expense |  |  |  |  |  |  |  |  |  | (40,639) | (44,559) | (52,435)
Other Expenses |  |  |  |  |  |  |  |  |  | (93,809) | (99,120) | (75,881)
Other non-operating income |  |  |  |  |  |  |  |  |  | 0 | 0 | 89,402
Income before income tax expense |  |  |  |  |  |  |  |  |  | 377,617 | 463,466 | 400,978
Depreciation expense related to property and equipment |  |  |  |  |  |  |  |  |  | 21,200 | 23,700 | 20,000
Acquisition and integration expenses |  |  |  |  |  |  |  |  |  | 0 | 7,138 | 33,169
Amortization expense for intangible assets |  |  |  |  |  |  |  |  |  | 37,100 | 50,000 | 41,200
Stock-based compensation expense |  |  |  |  |  |  |  |  |  | 33,946 | 31,155 | 28,607
GSG |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Other segment items |  |  |  |  |  |  |  |  |  | (1,789,231) | (1,628,952) | (1,403,678)
Reconciliation of profit (segment operating income): |  |  |  |  |  |  |  |  |  |  |  |
Impairment of goodwill |  |  |  |  |  |  |  |  |  | (92,416) |  |
Depreciation expense related to property and equipment |  |  |  |  |  |  |  |  |  | 3,000 | 3,300 | 3,300
Income (loss) from equity method investments |  |  |  |  |  |  |  |  |  | 1,100 | 1,600 | 2,800
CIG |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Other segment items |  |  |  |  |  |  |  |  |  | (2,130,713) | (2,083,374) | (1,871,899)
Reconciliation of profit (segment operating income): |  |  |  |  |  |  |  |  |  |  |  |
Impairment of goodwill |  |  |  |  |  |  |  |  |  | 0 |  |
Depreciation expense related to property and equipment |  |  |  |  |  |  |  |  |  | 17,800 | 20,100 | 16,300
Income (loss) from equity method investments |  |  |  |  |  |  |  |  |  | 2,500 | 3,300 | 3,200
Acquisition and integration expenses |  |  |  |  |  |  |  |  |  |  |  | 5,100
Operating Segments Excluding Intersegment Elimination |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 5,442,590 | 5,198,679 | 4,522,550
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 825,230 | 876,817 | 771,461
Operating Segments Excluding Intersegment Elimination | GSG |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 2,637,426 | 2,445,746 | 2,128,330
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 504,644 | 539,579 | 493,020
Operating Segments Excluding Intersegment Elimination | CIG |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 2,805,164 | 2,752,933 | 2,394,220
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 320,586 | 337,238 | 278,441
Intersegment Eliminations |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | (75,966) | (71,407) | (60,988)
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 75,966 | 71,407 | 60,988
Intersegment Eliminations | GSG |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | (36,483) | (37,609) | (30,559)
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 39,483 | 33,798 | 30,429
Intersegment Eliminations | CIG |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | (39,483) | (33,798) | (30,429)
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 36,483 | 37,609 | 30,559
Operating Segments |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 5,518,556 | 5,270,086 | 4,583,538
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 901,196 | 948,224 | 832,449
Segment operating income |  |  |  |  |  |  |  |  |  | 697,416 | 609,536 | 475,512
Reconciliation of profit (segment operating income): |  |  |  |  |  |  |  |  |  |  |  |
Right-of-use operating lease asset impairment |  |  |  |  |  |  |  |  |  |  |  | (15,100)
Operating Segments | GSG |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 2,673,909 | 2,483,355 | 2,158,889
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 544,127 | 573,377 | 523,449
Segment operating income |  |  |  |  |  |  |  |  |  | 340,551 | 281,026 | 231,762
Reconciliation of profit (segment operating income): |  |  |  |  |  |  |  |  |  |  |  |
Right-of-use operating lease asset impairment |  |  |  |  |  |  |  |  |  |  |  | (6,800)
Operating Segments | CIG |  |  |  |  |  |  |  |  |  |  |  |
Financial information concerning reportable segments |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 2,844,647 | 2,786,731 | 2,424,649
Total consolidated subcontractor costs |  |  |  |  |  |  |  |  |  | 357,069 | 374,847 | 309,000
Segment operating income |  |  |  |  |  |  |  |  |  | 356,865 | 328,510 | 243,750
Reconciliation of profit (segment operating income): |  |  |  |  |  |  |  |  |  |  |  |
Right-of-use operating lease asset impairment |  |  |  |  |  |  |  |  |  |  |  | (8,300)
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment |  |  |  |  |  |  |  |  |  |  |  |
Reconciliation of profit (segment operating income): |  |  |  |  |  |  |  |  |  |  |  |
Right-of-use operating lease asset impairment |  |  |  |  |  |  |  |  |  |  |  | (1,158)
Corporate |  |  |  |  |  |  |  |  |  |  |  |
Reconciliation of profit (segment operating income): |  |  |  |  |  |  |  |  |  |  |  |
Amortization expense for intangible assets |  |  |  |  |  |  |  |  |  | 37,100 | 50,000 | 41,200
Stock-based compensation expense |  |  |  |  |  |  |  |  |  | $ 19,300 | $ 18,500 | $ 16,400

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