Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended			87 Months Ended
	Sep. 30, 2011	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Net Income Loss Reconciliation [Line Items]
Impact of AMT Repeal on Current Taxes				$ 29,581
Change in Impact of AMT Repeal on Current Taxes			$ 1,902
AMT Related to Filing of 2017 Tax Return				5,536
AMT Receivable Resulting from TCJA			$ 37,019		$ 37,019
Impact of new Tax Law on Deferred Taxes				31,418
Net Impact of New Tax Law				$ 1,886
AMT Installment Payment End Date			Dec. 31, 2021
AACNetTaxableIncome					$ 1,508,000
Operating Loss Generated in Current Year		$ 143,000
TierABCCredit		(5,000)
TierABCredit		(10,000)
NOL allocated amount	$ 3,650,000	3,535,000
Tolling Payment to AFG		119,000
Tolling Payment Payable to AFG Outstanding Amount		28,000
Tolling Payment Payable to AFG		147,000
AACNetTaxableIncomeFromTierB		$ 1,029,000
Tier C Tolling Payment Payable to IRS		12.50%
Tier D Tolling Payments Payable to IRS		17.50%
Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		$ 2,285,000
Percentage Of Notional Federal Tax Liability	25.00%
AFG [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount		1,250,000
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
Minimum [Member] | Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2029
Minimum [Member] | AFG [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, 2040
Maximum [Member] | Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Dec. 31, 2040
Maximum [Member] | AFG [Member]
Net Income Loss Reconciliation [Line Items]
Operating Loss Carryforwards, Expiration Date		Jan. 01, 2034