Interim Pension and Other Postretirement Benefit Plan Information - Schedule of Net Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,045	$ 4,560
Interest cost	6,799	6,430
Expected return on assets	(7,113)	(6,917)
Amortization of prior service cost (credit)	(58)	(58)
Amortization of actuarial (gain) loss	1,608	3,089
Net periodic pension cost	5,281	7,104
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,702	3,020
Interest cost	2,961	2,727
Expected return on assets	(2,665)	(2,002)
Amortization of prior service cost (credit)	43	3
Amortization of actuarial (gain) loss	(2,045)	(1,618)
Net periodic pension cost	$ 996	$ 2,130