Debt - ABL Facility (Details) - USD ($)	Jun. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 47,000,000	$ 46,800,000
Remaining availability	$ 2,800,000	$ 700,000
ABL Facility
Debt Instrument [Line Items]
Weighted average interest rate	3.68%
Outstanding letters of credit	$ 72,900,000
Amount as collateral to the banking institution	722,900,000
ABL Facility | US Tranche
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	505,000,000.0
ABL Facility | Canadian Tranche
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	40,000,000.0
ABL Facility | FILO Tranche
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	30,000,000.0
Remaining availability	5,000,000
ABL Facility | U.S. and Canadian Tranches
Debt Instrument [Line Items]
Remaining availability	300,500,000
Term Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	655,000,000
Line of credit facility, increase in maximum borrowing capacity	$ 175,000,000.0