Derivative Instruments - Summary of Notional for VIE Derivatives Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount	$ 232,267	$ 213,585
Successor Ambac [Member] | Interest Rate Swaps [Member]
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount	1,669,298
Successor Ambac [Member] | Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount	4,356,549
Successor Ambac [Member] | Currency Swaps [Member]
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount	707,264
Successor Ambac [Member] | Credit Derivatives [Member]
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount	18,958
Predecessor Ambac [Member] | Interest Rate Swaps [Member]
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount		1,782,999
Predecessor Ambac [Member] | Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount		4,707,454
Predecessor Ambac [Member] | Currency Swaps [Member]
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount		755,438
Predecessor Ambac [Member] | Credit Derivatives [Member]
Schedule Of Notional For Variable Interest Entity Derivatives Outstanding [Line Items]
Derivative products, Notional Amount		$ 20,885