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Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended | 24 Months Ended | 36 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2011 | Dec. 31, 2017 | Dec. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2017
Net Income Loss Reconciliation [Line Items] |  |  |  |  |
TierABCCredit |  | $ 5,000 | $ 5,000 |  |
TierABCredit |  | (10,000) |  |  |
NOL allocated amount | $ 3,650,000 | 3,694,844 |  |  | $ 3,694,844
Tolling Payment to AFG |  | 637 | $ 71,454 | $ 100,145 | 637
Tolling Payment Payable to AFG |  | 30,496 |  | 28,691 | 30,496
Tolling Payment Payable to AFG |  | $ 31,133 |  | 28,691 | $ 31,133
Tier C Tolling Payment Payable to IRS |  | 12.50% |  |  | 12.50%
Tier D Tolling Payments Payable to IRS |  | 17.50% |  |  | 17.50%
Ambac Assurance [Member] |  |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |  |
AACNetTaxableIncome |  |  |  |  | $ 1,367,795
NOL allocated amount |  | $ 2,282,205 |  |  | 2,282,205
AACNetTaxableIncomeFromTierB |  |  |  | $ 607,124 | 888,795
Percentage Of Notional Federal Tax Liability | 25.00% |  |  |  |
AFG [Member] |  |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |  |
NOL allocated amount |  | 1,412,639 |  |  | 1,412,639
Percentage Of Notional Federal Tax Liability | 50.00% |  |  |  |
Tier A [Member] |  |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |  |
NOL allocated amount | $ 479,000 | $ 479,000 |  |  | 479,000
NOL applicable percentage |  | 15.00% |  |  |
Tier B [Member] |  |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |  |
NOL allocated amount | $ 1,057,000 | $ 1,057,000 |  |  | 1,057,000
NOL applicable percentage |  | 40.00% |  |  |
Tier C [Member] |  |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |  |
NOL allocated amount |  | $ 1,057,000 |  |  | 1,057,000
NOL applicable percentage |  | 10.00% |  |  |
Tier D [Member] |  |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |  |
NOL allocated amount |  | $ 1,057,000 |  |  | $ 1,057,000
NOL applicable percentage |  | 15.00% |  |  |

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