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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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