Income Taxes Income Taxes - NOL Usage Table (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended	24 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2011	Dec. 31, 2016	Dec. 31, 2015
Net Income Loss Reconciliation [Line Items]
Income Tax Examination, Penalties and Interest Accrued			$ 3,650,000
Post Determination Net Operating Loss	$ (32,084)
TierABCCredit	5,000
TierABCredit	10,000
NOL allocated amount	4,057,680
Tolling Payment to AFG				$ 100,145	$ 71,454
Ambac Assurance [Member]
Net Income Loss Reconciliation [Line Items]
Percentage Of Notional Federal Tax Liability			25.00%
AACNetTaxableIncome		$ 1,086,124
NOL allocated amount	2,595,960
AACNetTaxableIncomeFromTierB				$ 607,124
AFG [Member]
Net Income Loss Reconciliation [Line Items]
Percentage Of Notional Federal Tax Liability			50.00%
NOL allocated amount	1,389,646
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	$ 3,985,606