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 6 Months Ended
Mar. 31, 2023
Mar. 31, 2022
Mar. 31, 2023
Mar. 31, 2022
Amortization:        
Settlement losses     $ (24,242) $ (35,706)
Pension        
Net periodic benefit cost [Abstract]        
Service cost $ 31 $ 5 88 385
Interest cost 105 48 248 1,038
Expected return on plan assets 0 0 0 (1,042)
Amortization:        
Prior service credit 0 (66) 0 (19)
Net actuarial loss (6) 91 (16) 292
Settlement losses     1,271 30,856
Net benefit cost 130 78 1,591 31,510
Other Postretirement        
Net periodic benefit cost [Abstract]        
Service cost 19 41 38 82
Interest cost 161 103 322 206
Expected return on plan assets 0 0 0 0
Amortization:        
Prior service credit (91) (91) (182) (182)
Net actuarial loss (177) 0 (354) 0
Settlement losses     0 0
Net benefit cost $ (88) $ 53 $ (176) $ 106