Interim Pension and Other Postretirement Benefit Plan Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,653	$ 4,045
Interest cost	5,843	6,799
Expected return on assets	(7,079)	(7,113)
Amortization of prior service cost (credit)	(58)	(58)
Amortization of actuarial (gain) loss	(1,271)	1,608
Net periodic pension cost	2,088	5,281
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	3,366	2,702
Interest cost	2,653	2,961
Expected return on assets	(2,625)	(2,665)
Amortization of prior service cost (credit)	43	43
Amortization of actuarial (gain) loss	(334)	(2,045)
Net periodic pension cost	$ 3,103	$ 996