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 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Retirement Plan        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost $ 861 $ 1,023 $ 2,584 $ 3,069
Interest Cost 8,944 9,223 26,833 27,669
Expected Return on Plan Assets (14,710) (14,647) (44,131) (43,940)
Amortization of Prior Service Cost (Credit) 63 76 190 227
Amortization of (Gains) Losses 2,421 1,620 7,261 4,860
Net Amortization and Deferral for Regulatory Purposes (Including Volumetric Adjustments) [1] 152 85 (2,825) (3,026)
Net Periodic Benefit Cost (Income) (2,269) (2,620) (10,088) (11,141)
Other Post-Retirement Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 105 130 315 389
Interest Cost 3,836 3,625 11,508 10,876
Expected Return on Plan Assets (7,374) (6,536) (22,122) (19,608)
Amortization of Prior Service Cost (Credit) (65) (107) (195) (322)
Amortization of (Gains) Losses 152 9 456 28
Net Amortization and Deferral for Regulatory Purposes (Including Volumetric Adjustments) [1] 131 (447) (3,578) (5,333)
Net Periodic Benefit Cost (Income) $ (3,215) $ (3,326) $ (13,616) $ (13,970)
[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.