Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Balance Sheet (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	May 01, 2013	Apr. 30, 2013
Condensed Balance Sheet Statements, Captions [Line Items]
Tolling Payment Payable to AFG	$ 28,691	$ 70,911
Preferred stock, par value				$ 0.01
Preferred stock, shares authorized				20,000,000
Common stock, par value				$ 0.01
Common stock, shares authorized				130,000,000
Common stock, shares issued				45,000,000
Successor [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Fixed income securities, amortized cost	$ 5,435,385	$ 4,992,756
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Common stock, shares issued	45,194,954	45,044,222	45,000,000
Common stock, shares outstanding	45,194,954	45,044,222
Treasury stock, shares	22,458	8,202
Ambac Financial Group, Inc Parent Company Only [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000