Financial Instruments Measured at Fair Value - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	$ 12,517	$ 11,004
Carrying Value | Accrued Expenses and Other Current Liabilities | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	3,441	4,621
Carrying Value | Accrued Expenses and Other Current Liabilities | Fuel Hedge Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities		50
Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	28,056	46,193
Carrying Value | Other Liabilities | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	12,098	30,518
Investment Held by Rabbi Trust | Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	12,517	11,004
Investment Held by Rabbi Trust | Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	12,517	11,004
Level 1 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	12,517	11,004
Level 1 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	12,517	11,004
Level 1 | Investment Held by Rabbi Trust | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	12,517	11,004
Level 1 | Investment Held by Rabbi Trust | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	12,517	11,004
Level 2 Inputs | Accrued Expenses and Other Current Liabilities | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	3,441	4,621
Level 2 Inputs | Accrued Expenses and Other Current Liabilities | Fuel Hedge Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities		50
Level 2 Inputs | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	15,539	35,189
Level 2 Inputs | Other Liabilities | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	$ 12,098	$ 30,518