Fresh Start Financial Statement Reporting - Fresh Start Reorganized Condensed Consolidated Balance Sheet (Parenthetical) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Apr. 30, 2013
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Common stock, shares issued	45,000,000
Number of warrants issued	5,047,138
Pre-tax gain on extinguishment of obligations		$ 1,521,435
Internal Revenue Service [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Cash payments to IRS under the IRS Settlement	$ 101,900
Successor Ambac [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Common stock, shares issued	45,002,456	45,000,000
Number of warrants issued		5,047,138