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Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Taxes [Line Items]
Effective tax rate (ETR) from continuing operations	23.80%		(2609.50%)
Statutory federal tax rate	21.00%		35.00%	21.00%
Discrete net tax benefit in connection with initial analysis of tax act			$ 22,400			$ 22,400
Decrease in net deferred tax liabilities excluding valuation allowance						22,000
Estimated increase to valuation allowance						500
Adjustment to deferred income tax benefit	$ 900					21,500
AMT credits	2,500
Income tax (benefit) expense	5,949		$ (21,789)
State net operating loss carryforwards		$ 900		$ 900		900
Domestic Tax Authority [Member] | 2027-2037 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		415,100		415,100		$ 415,100
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year						2019
State and Local Jurisdiction [Member] | 2019-2038 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		199,600		$ 199,600		$ 199,600
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						2019
Maximum [Member] | Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year						2037
Maximum [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year						2038
AMT Credit Carryover [Member]
Income Taxes [Line Items]
Income tax (benefit) expense	$ (100)	$ 100
Scenario, Plan [Member]
Income Taxes [Line Items]
Statutory federal tax rate					21.00%

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