Fresh Start Financial Statement Reporting - Schedule of Liabilities Subject to Compromise (Detail) (Predecessor Ambac [Member], USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Dec. 31, 2012
Predecessor Ambac [Member]
Fresh-Start Adjustment [Line Items]
Debt obligations and accrued interest payable		$ 1,690,312
Other		14,592
Consolidated liabilities subject to compromise	1,704,641	1,704,904
Payable to non-debtor subsidiaries		35
Debtor's Liabilities subject to compromise		$ 1,704,939