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, 2018
Mar. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Pension        
Net periodic benefit cost [Abstract]        
Service cost $ 2,039 $ 2,138 $ 4,078 $ 4,276
Interest cost 2,049 1,841 4,098 3,682
Expected return on plan assets (2,534) (2,312) (5,068) (4,624)
Amortization:        
Prior service cost (35) (45) (70) (90)
Net actuarial loss 1,752 2,509 3,504 5,018
Net benefit cost 3,271 4,131 6,542 8,262
Defined Benefit Plan, Expected Future Employer Contributions [Abstract]        
Additional contributions expected in fiscal 2018: 10,000   10,000  
Other Postretirement        
Net periodic benefit cost [Abstract]        
Service cost 84 98 168 196
Interest cost 158 157 316 314
Expected return on plan assets 0 0 0 0
Amortization:        
Prior service cost (49) (49) (98) (98)
Net actuarial loss 0 0 0 0
Net benefit cost 193 $ 206 386 $ 412
Defined Benefit Plan, Expected Future Employer Contributions [Abstract]        
Other Postretirement     862  
Additional contributions expected in fiscal 2018: 182   182  
Supplemental retirement plan        
Defined Benefit Plan, Expected Future Employer Contributions [Abstract]        
Pension     369  
Additional contributions expected in fiscal 2018: $ 396   $ 396