Quarterly report pursuant to Section 13 or 15(d)

Pension and Other Postretirement Benefit Plans - Net Periodic Pension and Other Postretirement Benefit Cost (Details)

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Pension and Other Postretirement Benefit Plans - Net Periodic Pension and Other Postretirement Benefit Cost (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2023
Jun. 30, 2022
Jun. 30, 2023
Jun. 30, 2022
Amortization:        
Settlement losses     $ (24,242) $ (35,706)
Pension        
Net periodic benefit cost [Abstract]        
Service cost $ 31 $ 4 119 389
Interest cost 106 48 354 1,086
Expected return on plan assets 0 0 0 (1,042)
Amortization:        
Prior service credit 0 (66) 0 (85)
Net actuarial loss (5) 88 (21) 380
Settlement losses     1,271 30,856
Net benefit cost 132 74 1,723 31,584
Other Postretirement        
Net periodic benefit cost [Abstract]        
Service cost 19 42 57 124
Interest cost 161 102 483 308
Expected return on plan assets 0 0 0 0
Amortization:        
Prior service credit (92) (91) (274) (273)
Net actuarial loss (177) 0 (531) 0
Settlement losses     0 0
Net benefit cost $ (89) $ 53 $ (265) $ 159