Fresh Start Financial Statement Reporting - Cancellation of Equity Accounts Attributable to Shareholders and Fair Value Adjustment of Noncontrolling Interests (Detail) (Predecessor Ambac [Member], USD $) In Thousands, unless otherwise specified	Apr. 30, 2013
Predecessor Ambac [Member]
Fresh-Start Adjustment [Line Items]
Common stock	$ (3,080)
Additional paid-in-capital	(2,172,027)
Accumulated other comprehensive income	(800,260)
Accumulated deficit	2,948,275
Common stock held in treasury at cost	410,695
Noncontrolling interest fair value adjustment	(383,603)
Net adjustment