Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Thousands	6 Months Ended	9 Months Ended
	Jun. 30, 2019	Sep. 30, 2011	Mar. 31, 2019	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				$ 16,513
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	$ 53,122
Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
AACNetTaxableIncome	60,991
NOL allocated amount	2,224,112
Afg [Member]
Net Income Loss Reconciliation [Line Items]
NOL allocated amount	$ 1,252,714
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			$ 3,476,826
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