Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Stockholders' Equity (Detail) - USD ($) $ in Thousands	4 Months Ended	8 Months Ended		12 Months Ended
	Apr. 30, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	May. 01, 2013
Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ 460,415	$ 460,415	$ 1,673,735	$ 978,422
Issuance of new equity in connection with emergence from Chapter 11						$ 185,000
Total comprehensive income		516,904	516,904	287,252	691,884
Stock-based compensation		(1,106)	(1,106)	(3,105)	(3,450)
Cost of shares acquired				(374)	(37)
Payments for Repurchase of Warrants			0	5,375	0
Warrants exercised		16		3	16
Cost of shares acquired		19
Ending balance	$ 460,415	978,422	978,422	1,958,346	1,673,735
Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(3,246,967)		275,415
Total comprehensive income	3,522,382
Stock-based compensation	60
Cost of shares acquired	60
Payments for Repurchase of Warrants	0
Elimination of Predecessor Ambac Shareholder equity accounts	0
Ending balance	275,415
Retained Earnings/Accumulated Deficit [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		989,290	505,219
Issuance of new equity in connection with emergence from Chapter 11						0
Total comprehensive income		505,219		493,403	484,071
Stock-based compensation		0		0	0
Cost of shares acquired				(312)	0
Payments for Repurchase of Warrants				(3,942)
Warrants exercised		0		0	0
Cost of shares acquired		0
Ending balance		505,219	505,219	1,478,439	989,290
Retained Earnings/Accumulated Deficit [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(6,297,264)		0
Total comprehensive income	3,349,049
Stock-based compensation	60
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	(2,948,275)
Ending balance	0
Accumulated Other Comprehensive Income (Loss) [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		220,283	11,661
Issuance of new equity in connection with emergence from Chapter 11						0
Total comprehensive income		11,661		(205,068)	208,622
Stock-based compensation		0		0	0
Cost of shares acquired				0	0
Payments for Repurchase of Warrants				0
Warrants exercised		0		0	0
Cost of shares acquired		0
Ending balance		11,661	11,661	15,215	220,283
Accumulated Other Comprehensive Income (Loss) [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	625,385		0
Total comprehensive income	174,875
Stock-based compensation	0
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	800,260
Ending balance	0
Preferred Stock [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		0	0
Issuance of new equity in connection with emergence from Chapter 11						0
Total comprehensive income		0		0	0
Stock-based compensation		0		0	0
Cost of shares acquired				0	0
Payments for Repurchase of Warrants				0
Warrants exercised		0		0	0
Cost of shares acquired		0
Ending balance		0	0	0	0
Preferred Stock [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0		0
Total comprehensive income	0
Stock-based compensation	0
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	0
Ending balance	0
Common Stock [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		450		450	450
Issuance of new equity in connection with emergence from Chapter 11						450
Total comprehensive income		0		0	0
Stock-based compensation		0		0	0
Cost of shares acquired				0	0
Payments for Repurchase of Warrants				0
Warrants exercised		0		0	0
Cost of shares acquired		0
Ending balance		450	450	450	450
Common Stock [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	3,080		0
Total comprehensive income	0
Stock-based compensation	0
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	3,080
Ending balance	0
Additional Paid-in Capital [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		184,550		189,138	185,672
Issuance of new equity in connection with emergence from Chapter 11						184,550
Total comprehensive income		0		0	0
Stock-based compensation		(1,106)		(3,105)	(3,450)
Cost of shares acquired				0	0
Payments for Repurchase of Warrants				(1,433)
Warrants exercised		16		3	16
Cost of shares acquired		0
Ending balance		185,672	185,672	190,813	189,138
Additional Paid-in Capital [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	2,172,027		0
Total comprehensive income	0
Stock-based compensation	0
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	2,172,027
Ending balance	0
Common Stock Held in Treasury, at Cost [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		(56)	(19)
Issuance of new equity in connection with emergence from Chapter 11						0
Total comprehensive income		0		0	0
Stock-based compensation		0		0	0
Cost of shares acquired				(62)	(37)
Payments for Repurchase of Warrants				0
Warrants exercised		0		0	0
Cost of shares acquired		19
Ending balance		(19)	(19)	(118)	(56)
Common Stock Held in Treasury, at Cost [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(410,755)		0
Total comprehensive income	0
Stock-based compensation	0
Cost of shares acquired	60
Elimination of Predecessor Ambac Shareholder equity accounts	(410,695)
Ending balance	0
Ambac Financial Group, Inc Parent Company Only [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		185,000		1,399,105	702,983
Issuance of new equity in connection with emergence from Chapter 11						185,000
Total comprehensive income			516,880	288,335	692,693
Stock-based compensation			(1,106)	(3,105)	(3,450)
Cost of shares acquired				(374)	(37)
Payments for Repurchase of Warrants				(5,375)
Warrants exercised			16	3	16
Cost of shares acquired			(19)
Ending balance		702,983	702,983	1,684,799	1,399,105
Ambac Financial Group, Inc Parent Company Only [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(3,907,527)		0
Total comprehensive income	3,523,924
Stock-based compensation	(60)
Cost of shares acquired	60
Elimination of Predecessor Ambac Shareholder equity accounts	383,603
Ending balance	0
Ambac Financial Group, Inc Parent Company Only [Member] | Retained Earnings/Accumulated Deficit [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		989,290	505,219
Issuance of new equity in connection with emergence from Chapter 11						0
Total comprehensive income			505,219	493,403	484,071
Stock-based compensation			0	0	0
Cost of shares acquired				(312)	0
Payments for Repurchase of Warrants				(3,942)
Warrants exercised			0	0	0
Cost of shares acquired			0
Ending balance		505,219	505,219	1,478,439	989,290
Ambac Financial Group, Inc Parent Company Only [Member] | Retained Earnings/Accumulated Deficit [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(6,297,264)		0
Total comprehensive income	3,349,049
Stock-based compensation	(60)
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	2,948,275
Ending balance	0
Ambac Financial Group, Inc Parent Company Only [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		220,283	11,661
Issuance of new equity in connection with emergence from Chapter 11						0
Total comprehensive income			11,661	(205,068)	208,622
Stock-based compensation			0	0	0
Cost of shares acquired				0	0
Payments for Repurchase of Warrants				0
Warrants exercised			0	0	0
Cost of shares acquired			0
Ending balance		11,661	11,661	15,215	220,283
Ambac Financial Group, Inc Parent Company Only [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	625,385		0
Total comprehensive income	174,875
Stock-based compensation	0
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	(800,260)
Ending balance	0
Ambac Financial Group, Inc Parent Company Only [Member] | Preferred Stock [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		0	0
Issuance of new equity in connection with emergence from Chapter 11						0
Total comprehensive income			0	0	0
Stock-based compensation			0	0	0
Cost of shares acquired				0	0
Payments for Repurchase of Warrants				0
Warrants exercised			0	0	0
Cost of shares acquired			0
Ending balance		0	0	0	0
Ambac Financial Group, Inc Parent Company Only [Member] | Preferred Stock [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0		0
Total comprehensive income	0
Stock-based compensation	0
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	0
Ending balance	0
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		450		450	450
Issuance of new equity in connection with emergence from Chapter 11						450
Total comprehensive income			0	0	0
Stock-based compensation			0	0	0
Cost of shares acquired				0	0
Payments for Repurchase of Warrants				0
Warrants exercised			0	0	0
Cost of shares acquired			0
Ending balance		450	450	450	450
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	3,080		0
Total comprehensive income	0
Stock-based compensation	0
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	(3,080)
Ending balance	0
Ambac Financial Group, Inc Parent Company Only [Member] | Additional Paid-in Capital [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		184,550		189,138	185,672
Issuance of new equity in connection with emergence from Chapter 11						184,550
Total comprehensive income			0	0	0
Stock-based compensation			(1,106)	(3,105)	(3,450)
Cost of shares acquired				0	0
Payments for Repurchase of Warrants				(1,433)
Warrants exercised			16	3	16
Cost of shares acquired			0
Ending balance		185,672	185,672	190,813	189,138
Ambac Financial Group, Inc Parent Company Only [Member] | Additional Paid-in Capital [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	2,172,027		0
Total comprehensive income	0
Stock-based compensation	0
Cost of shares acquired	0
Elimination of Predecessor Ambac Shareholder equity accounts	(2,172,027)
Ending balance	0
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock Held in Treasury, at Cost [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		(56)	(19)
Issuance of new equity in connection with emergence from Chapter 11						$ 0
Total comprehensive income			0	0	0
Stock-based compensation			0	0	0
Cost of shares acquired				(62)	(37)
Payments for Repurchase of Warrants				0
Warrants exercised			0	0	0
Cost of shares acquired			(19)
Ending balance		$ (19)	(19)	$ (118)	$ (56)
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock Held in Treasury, at Cost [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(410,755)		$ 0
Total comprehensive income	0
Stock-based compensation	0
Cost of shares acquired	60
Elimination of Predecessor Ambac Shareholder equity accounts	410,695
Ending balance	$ 0