Interim Pension and Other Postretirement Benefit Plan Information - Narrative (Details) - USD ($) $ in Thousands			3 Months Ended				9 Months Ended
	Jun. 05, 2018	Mar. 01, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Supplemental Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Settlements loss			$ 900	$ 2,400
Discount rate	4.29%	4.12%	4.29%		3.89%	3.73%	4.29%	3.73%
Increase our net periodic pension cost	$ 200	$ 100
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlements loss			$ 0			$ 0	$ 0	$ 0
Discount rate			3.89%			3.73%	3.89%	3.73%
Benefit plan contribution amount							$ 11,400
Other Benefits | Minimum
Defined Benefit Plan Disclosure [Line Items]
Benefit plan expected contribution amount			$ 10,000				10,000
Other Benefits | Maximum
Defined Benefit Plan Disclosure [Line Items]
Benefit plan expected contribution amount			$ 20,000				$ 20,000