Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2011	Dec. 31, 2017
Net Income Loss Reconciliation [Line Items]
Tolling Payment Payable to AFG	$ 11,021		$ 30,496
NOL allocated amount		$ 3,650,000
Tier C Tolling Payments Payable to IRS	12.50%
Tier D Tolling Payments Payable to IRS	17.50%
Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
AACNetTaxableIncome	$ (131,201)
NOL allocated amount	2,151,004
Afg [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount	1,398,610
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%
Domestic Tax Authority [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount	$ 3,549,614