Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013 Successor Ambac [Member]	Dec. 31, 2012 Predecessor Ambac [Member]
Fixed income securities, amortized cost	$ 5,795,824	$ 4,751,824
Fixed income securities pledged as collateral, amortized cost	140,216	265,517
Short-term investments, amortized cost	$ 549,233	$ 661,219
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	4,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	650,000,000
Common stock, shares issued	45,002,524	308,016,674
Common stock, shares outstanding	45,002,524	308,016,674
Treasury stock, shares		5,580,657