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Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended			12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018
Income Taxes [Line Items]
Effective tax rate (ETR) from continuing operations	23.90%	37.00%		228.20%		37.20%
Discrete net tax benefit in connection with initial analysis of tax act				$ (21.4)
Decrease in net deferred tax liabilities				(21.4)
Adjustment to deferred income tax benefit				(21.4)
Net operating loss carryforward	$ 411.2		$ 411.2	411.2
State net operating loss carryforwards	$ 20.1		20.1	$ 20.1
Estimated increase in net operating loss carryforward			$ 111.4
Domestic Tax Authority [Member] | 2027-2036 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards					$ 299.8
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year			2018
State and Local Jurisdiction [Member] | 2018-2037 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards					$ 172.3
Subsequent Event [Member]
Income Taxes [Line Items]
Federal corporate tax rate							21.00%
Blended corporate tax rate							24.53%
Minimum [Member] | Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year					2027
Minimum [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year					2018
Maximum [Member] | Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year					2036
Maximum [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year					2037

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