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Income Taxes - Textual (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Income Taxes - Textual (Details) - USD ($) $ in Millions	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Taxes [Abstract]
Effective tax rate		35.20%	34.50%	33.20%
Increase (Decrease) in Income Taxes Payable	$ (58.2)
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	5.3
Federal statutory rate		35.00%
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 26.2	$ 40.1
Unrecognized tax benefits		0.0	0.0	$ 0.0
Accrued interest related to unrecognized tax benefits		0.0	0.0	0.0
Accrued penalties related to unrecognized tax benefits		0.0	0.0	0.0
Increase (Decrease) in Deferred Income Taxes		(110.8)	$ (75.3)	$ (3.1)
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		26.2
State [Member] \| Tax Credit Carryforward Amount to Expire [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carry forwards		1.4
State [Member] \| Tax Credit Carryforward Amount with No Expiration [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carry forwards		1.1
State [Member] \| NOL Carryforwards to Expire in One to Five Years [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration		3.8
State [Member] \| NOL Carryforwards to Expire in Six to Ten Years [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration		2.7
State [Member] \| Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration		$ 19.7
Sales Revenue, Net [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes	(13.4)
Inventories [Member]
Operating Loss Carryforwards [Line Items]
Increase (Decrease) in Deferred Income Taxes	$ (50.1)