Fair Value Measurements and Derivatives Instruments - Summary of Effects on Consolidated Financial Statements of Designated As Cash Flow Hedges (Details) - Cash Flow Hedges - Designated - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Income (loss) recognized in Other comprehensive income (effective portion)	$ 2,047	$ (2,794)	$ 9,127	$ 5,529
Interest Rate Swap | Interest Expense
Derivative Instruments Gain Loss [Line Items]
Loss recognized in Interest expense (ineffective portion)	(2)	(4)	(1)	(3)
Net (loss) income reclassified from Accumulated other comprehensive loss into Interest expense or cost of services provided	$ (2,513)	(2,966)	(7,344)	(6,770)
Fuel Swap Contracts
Derivative Instruments Gain Loss [Line Items]
Income (loss) recognized in Other comprehensive income (effective portion)		(201)	57	(1,100)
Fuel Swap Contracts | Cost of Services Provided
Derivative Instruments Gain Loss [Line Items]
Loss recognized in Interest expense (ineffective portion)		23		(22)
Net (loss) income reclassified from Accumulated other comprehensive loss into Interest expense or cost of services provided		$ (90)	$ 7	$ (2,146)