Fair Value Measurements and Derivatives Instruments - Additional Information (Details)	9 Months Ended
	Jun. 30, 2020 USD ($) Fuel	Sep. 30, 2019 USD ($)
Interest Rate Contracts
Derivative [Line Items]
Notional amount	$ 980,000,000.0	$ 1,000,000,000.0
Interest Rate Swaps
Derivative [Line Items]
Net deferred losses on interest rate swap net of taxes expected to be recognized over the next six/12 months	8,100,000
Fuel Swap Contracts
Derivative [Line Items]
Notional amount	13,000,000.0
Net deferred losses on interest rate swap net of taxes expected to be recognized over the next six/12 months	$ 1,600,000
Number of outstanding fuel contracts | Fuel	5
Maximum
Derivative [Line Items]
Percentage of participants compensation deferred	70.00%