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v3.25.3

Fair Values and Percentage of Company's Pension Plan Assets by Asset Category (Detail) - USD ($) $ in Thousands | Sep. 30, 2025 | Sep. 30, 2024
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of the Partnership's pension plan assets |  | 100.00% | 100.00%
Significant Other Observable Inputs Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Partnership's pension plan assets |  | $ 38,632 | $ 41,330
Quoted Prices in Active Markets for Identical Assets Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Partnership's pension plan assets |  | $ 4,913 | $ 5,660
Corporate and U.S. government bond fund |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of the Partnership's pension plan assets | [1] | 88.70% | 88.00%
Corporate and U.S. government bond fund | Significant Other Observable Inputs Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Partnership's pension plan assets | [1] | $ 38,632 | $ 41,330
U.S. large-cap equity |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of the Partnership's pension plan assets | [1] | 11.00% | 12.00%
U.S. large-cap equity | Quoted Prices in Active Markets for Identical Assets Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Partnership's pension plan assets | [1] | $ 4,797 | $ 5,660
Cash |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of the Partnership's pension plan assets |  | 0.30% | 0.00%
Cash | Quoted Prices in Active Markets for Identical Assets Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Partnership's pension plan assets |  | $ 116 | $ 0
[1] | Represent investments in Principal funds at September 30, 2025 and September 30, 2024.

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