Quarterly report pursuant to Section 13 or 15(d)

Pension and Other Postretirement Benefit Plans (Details)

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Pension and Other Postretirement Benefit Plans (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Mar. 31, 2019
Mar. 31, 2018
Pension        
Net periodic benefit cost [Abstract]        
Service cost $ 2,000 $ 2,039 $ 4,000 $ 4,078
Interest cost 2,301 2,049 4,602 4,098
Expected return on plan assets (2,596) (2,534) (5,192) (5,068)
Amortization:        
Prior service cost (46) (35) (92) (70)
Net actuarial loss (gain) 1,100 1,752 2,161 3,504
Net benefit cost 2,759 3,271 5,479 6,542
Other Postretirement        
Net periodic benefit cost [Abstract]        
Service cost 61 84 122 168
Interest cost 180 158 360 316
Expected return on plan assets 0 0 0 0
Amortization:        
Prior service cost (49) (49) (98) (98)
Net actuarial loss (gain) (15) 0 (30) 0
Net benefit cost 177 $ 193 354 $ 386
Contributions during the six months ended March 31, 2019:        
Other Postretirement     757  
Additional contributions expected in fiscal 2019:        
Supplemental retirement plan 318   318  
Supplemental retirement plan        
Contributions during the six months ended March 31, 2019:        
Pension     391  
Additional contributions expected in fiscal 2019:        
Supplemental retirement plan $ 466   $ 466