v3.26.1
Retirement Plan and Other Post-Retirement Benefits (Schedule of Components of Net Periodic Benefit Cost) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Retirement Plan        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost $ 861 $ 1,023 $ 1,723 $ 2,046
Interest Cost 8,944 9,223 17,889 18,446
Expected Return on Plan Assets (14,710) (14,647) (29,421) (29,293)
Amortization of Prior Service Cost (Credit) 63 76 126 151
Amortization of (Gains) Losses 2,421 1,620 4,841 3,240
Net Amortization and Deferral for Regulatory Purposes (Including Volumetric Adjustments) [1] (2,879) (2,946) (2,977) (3,111)
Net Periodic Benefit Cost (Income) (5,300) (5,651) (7,819) (8,521)
Other Post-Retirement Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 105 130 210 259
Interest Cost 3,836 3,625 7,672 7,251
Expected Return on Plan Assets (7,374) (6,536) (14,748) (13,072)
Amortization of Prior Service Cost (Credit) (65) (107) (130) (214)
Amortization of (Gains) Losses 152 9 304 18
Net Amortization and Deferral for Regulatory Purposes (Including Volumetric Adjustments) [1] (3,560) (4,158) (3,709) (4,885)
Net Periodic Benefit Cost (Income) $ (6,906) $ (7,037) $ (10,401) $ (10,643)
[1] The Company’s policy is to record retirement plan and other post-retirement benefit costs in the Utility segment on a volumetric basis to reflect the fact that the Utility segment experiences higher throughput of natural gas in the winter months and lower throughput of natural gas in the summer months.