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Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2019 | Sep. 30, 2011 | Dec. 31, 2018 | Dec. 31, 2017
Net Income Loss Reconciliation [Line Items] |  |  |  |
Tolling Payment Payable to AFG Generated in Prior Years | $ 44,381 |  |  | $ 27,868
Tolling Payment Payable to AFG, Gross |  |  | $ 13,885 |
NOL allocated amount |  | $ 3,650,000 |  |
Tier C Tolling Payments Payable to IRS | 12.50% |  |  |
Tier D Tolling Payments Payable to IRS | 17.50% |  |  |
Current Year Loss Attributed to Tier B | $ 80,197 |  |  |
Ambac Assurance [Member] |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |
AACNetTaxableIncome | 89,326 |  |  |
NOL allocated amount | 2,252,447 |  |  |
Afg [Member] |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |
NOL allocated amount | $ 1,251,453 |  |  |
Tier A [Member] |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |
NOL allocated amount |  | $ 479,000 |  |
NOL applicable percentage |  | 15.00% |  |
Tier B [Member] |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |
NOL allocated amount |  | $ 1,057,000 |  |
NOL applicable percentage |  | 40.00% |  |
Tier C [Member] |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |
NOL allocated amount |  | $ 1,057,000 |  |
NOL applicable percentage |  | 10.00% |  |
Tier D [Member] |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |
NOL allocated amount |  | $ 1,057,000 |  |
NOL applicable percentage |  | 15.00% |  |
Minimum [Member] |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |
Operating Loss Carryforwards, Expiration Date | Dec. 31, 2029 |  |  |
Maximum [Member] |  |  |  |
Net Income Loss Reconciliation [Line Items] |  |  |  |
Operating Loss Carryforwards, Expiration Date | Dec. 31, 2032 |  |  |

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