Defined Benefit Pension and Other Postretirement Plans - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans
Contribution made to pension and post-retirement plans			$ 6,300,000	$ 5,000,000.0
Expected contribution to pension plan during remainder of fiscal year		$ 6,000,000.0		6,000,000.0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans
Contribution made to pension and post-retirement plans			0	0
Defined benefit plan, net periodic benefit cost (credit)	$ (100,000)	(100,000)	(100,000)	(200,000)
Unfunded Plan | Nonqualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Defined benefit plan, net periodic benefit cost (credit)	$ 0	$ 0	$ 0	$ 0