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Defined Pension Benefit Obligations - Narrative (Details) $ in Thousands |  | 1 Months Ended | 3 Months Ended | 6 Months Ended
--- | --- | --- | --- | ---
Dec. 15, 2017 | Dec. 31, 2017 USD ($) | Mar. 30, 2018 USD ($) Plan | Mar. 31, 2017 USD ($) | Mar. 30, 2018 USD ($) Plan | Mar. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Settlement loss |  |  | $ 0 | $ (41) | $ (3,819) | $ (84)
CH2M HILL Companies, Ltd. |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit pension plan assets |  |  | 1,100,000 |  | 1,100,000 |
Defined benefit pension plan liabilities |  |  | $ 1,200,000 |  | $ 1,200,000 |
Business acquisition effective date of acquisition | Dec. 15, 2017 |  |  |  |  |
U.S. | Sverdrup Pension Plan |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Settlement loss |  | $ 3,800 |  |  |  |
U.S. | CH2M HILL Companies, Ltd. |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Number of noncontributory defined benefit pension plans | Plan |  |  | 3 |  | 3 |

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