Fair Value Measurements and Derivatives Instruments - Additional Information (Details)	6 Months Ended
	Mar. 31, 2020 USD ($) Fuel	Sep. 30, 2019 USD ($)
Interest Rate Contracts
Derivative [Line Items]
Notional amount	$ 980,000,000	$ 1,000,000,000
Interest Rate Swaps
Derivative [Line Items]
Net deferred losses on interest rate swap net of taxes expected to be recognized over the next 12 months	12,900,000
Fuel Swap Contracts
Derivative [Line Items]
Notional amount	11,000,000
Net deferred losses on interest rate swap net of taxes expected to be recognized over the next 12 months	$ 3,800,000
Number of outstanding fuel contracts | Fuel	4
Maximum
Derivative [Line Items]
Percentage of participants compensation deferred	70.00%