Special Purpose Entities, Including Variable Interest Entities - Supplemental Information About Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities (Detail) (Variable Interest Entity [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013 Successor Ambac [Member]	Dec. 31, 2012 Predecessor Ambac [Member]
Variable Interest Entities [Line Items]
Loans, Estimated fair value	$ 13,820,878	$ 15,359,073
Long-term debt, Estimated fair value	14,262,734	15,200,538
Loans, Unpaid principal balance	12,682,823	13,995,141
Long-term debt, Unpaid principal balance	$ 14,846,432	$ 15,460,530