Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified					9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended				4 Months Ended		3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended				4 Months Ended		3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended				4 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended					4 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended					4 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended					4 Months Ended		3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended				4 Months Ended		3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended				4 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Successor Ambac [Member]	Dec. 31, 2013 Successor Ambac [Member]	Sep. 30, 2014 Successor Ambac [Member] CLO [Member]	Dec. 31, 2013 Successor Ambac [Member] CLO [Member]	Sep. 30, 2014 Successor Ambac [Member] Other [Member]	Dec. 31, 2013 Successor Ambac [Member] Other [Member]	Sep. 30, 2014 Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2013 Investment Type [Member] Successor Ambac [Member]	Apr. 30, 2013 Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2013 Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2014 Investment Type [Member] Successor Ambac [Member]	Jun. 30, 2014 Investment Type [Member] Successor Ambac [Member]	Dec. 31, 2013 Investment Type [Member] Successor Ambac [Member]	Jun. 30, 2013 Investment Type [Member] Successor Ambac [Member]	Apr. 30, 2013 Investment Type [Member] Predecessor [Member]	Dec. 31, 2012 Investment Type [Member] Predecessor [Member]	Sep. 30, 2014 Investment Type [Member] Corporate Debt Securities [Member] Successor Ambac [Member]	Sep. 30, 2013 Investment Type [Member] Corporate Debt Securities [Member] Successor Ambac [Member]	Apr. 30, 2013 Investment Type [Member] Corporate Debt Securities [Member] Successor Ambac [Member]	Sep. 30, 2013 Investment Type [Member] Corporate Debt Securities [Member] Successor Ambac [Member]	Sep. 30, 2014 Investment Type [Member] Corporate Debt Securities [Member] Successor Ambac [Member]	Jun. 30, 2014 Investment Type [Member] Corporate Debt Securities [Member] Successor Ambac [Member]	Dec. 31, 2013 Investment Type [Member] Corporate Debt Securities [Member] Successor Ambac [Member]	Jun. 30, 2013 Investment Type [Member] Corporate Debt Securities [Member] Successor Ambac [Member]	Apr. 30, 2013 Investment Type [Member] Corporate Debt Securities [Member] Predecessor [Member]	Dec. 31, 2012 Investment Type [Member] Corporate Debt Securities [Member] Predecessor [Member]	Sep. 30, 2014 Investment Type [Member] Collateralized Debt Obligations [Member] Successor Ambac [Member]	Sep. 30, 2013 Investment Type [Member] Collateralized Debt Obligations [Member] Successor Ambac [Member]	Apr. 30, 2013 Investment Type [Member] Collateralized Debt Obligations [Member] Successor Ambac [Member]	Sep. 30, 2013 Investment Type [Member] Collateralized Debt Obligations [Member] Successor Ambac [Member]	Sep. 30, 2014 Investment Type [Member] Collateralized Debt Obligations [Member] Successor Ambac [Member]	Jun. 30, 2014 Investment Type [Member] Collateralized Debt Obligations [Member] Successor Ambac [Member]	Dec. 31, 2013 Investment Type [Member] Collateralized Debt Obligations [Member] Successor Ambac [Member]	Jun. 30, 2013 Investment Type [Member] Collateralized Debt Obligations [Member] Successor Ambac [Member]	Apr. 30, 2013 Investment Type [Member] Collateralized Debt Obligations [Member] Predecessor [Member]	Dec. 31, 2012 Investment Type [Member] Collateralized Debt Obligations [Member] Predecessor [Member]	Sep. 30, 2014 Derivative [Member] Successor Ambac [Member]	Sep. 30, 2013 Derivative [Member] Successor Ambac [Member]	Sep. 30, 2013 Derivative [Member] Successor Ambac [Member]	Sep. 30, 2014 Derivative [Member] Successor Ambac [Member]	Jun. 30, 2014 Derivative [Member] Successor Ambac [Member]	Dec. 31, 2013 Derivative [Member] Successor Ambac [Member]	Jun. 30, 2013 Derivative [Member] Successor Ambac [Member]	Apr. 30, 2013 Derivative [Member] Successor Ambac [Member]	Apr. 30, 2013 Derivative [Member] Predecessor [Member]	Dec. 31, 2012 Derivative [Member] Predecessor [Member]	Sep. 30, 2014 Derivative [Member] Interest Rate Swap [Member] Successor Ambac [Member]	Sep. 30, 2013 Derivative [Member] Interest Rate Swap [Member] Successor Ambac [Member]	Sep. 30, 2013 Derivative [Member] Interest Rate Swap [Member] Successor Ambac [Member]	Sep. 30, 2014 Derivative [Member] Interest Rate Swap [Member] Successor Ambac [Member]	Jun. 30, 2014 Derivative [Member] Interest Rate Swap [Member] Successor Ambac [Member]	Dec. 31, 2013 Derivative [Member] Interest Rate Swap [Member] Successor Ambac [Member]	Jun. 30, 2013 Derivative [Member] Interest Rate Swap [Member] Successor Ambac [Member]	Apr. 30, 2013 Derivative [Member] Interest Rate Swap [Member] Successor Ambac [Member]	Apr. 30, 2013 Derivative [Member] Interest Rate Swap [Member] Predecessor [Member]	Dec. 31, 2012 Derivative [Member] Interest Rate Swap [Member] Predecessor [Member]	Sep. 30, 2014 Derivative [Member] Credit Derivative [Member] Successor Ambac [Member]	Sep. 30, 2013 Derivative [Member] Credit Derivative [Member] Successor Ambac [Member]	Sep. 30, 2013 Derivative [Member] Credit Derivative [Member] Successor Ambac [Member]	Sep. 30, 2014 Derivative [Member] Credit Derivative [Member] Successor Ambac [Member]	Jun. 30, 2014 Derivative [Member] Credit Derivative [Member] Successor Ambac [Member]	Dec. 31, 2013 Derivative [Member] Credit Derivative [Member] Successor Ambac [Member]	Jun. 30, 2013 Derivative [Member] Credit Derivative [Member] Successor Ambac [Member]	Apr. 30, 2013 Derivative [Member] Credit Derivative [Member] Successor Ambac [Member]	Apr. 30, 2013 Derivative [Member] Credit Derivative [Member] Predecessor [Member]	Dec. 31, 2012 Derivative [Member] Credit Derivative [Member] Predecessor [Member]	Sep. 30, 2014 Asset-backed Securities [Member] Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2013 Asset-backed Securities [Member] Investment Type [Member] Successor Ambac [Member]	Apr. 30, 2013 Asset-backed Securities [Member] Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2013 Asset-backed Securities [Member] Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2014 Asset-backed Securities [Member] Investment Type [Member] Successor Ambac [Member]	Jun. 30, 2014 Asset-backed Securities [Member] Investment Type [Member] Successor Ambac [Member]	Dec. 31, 2013 Asset-backed Securities [Member] Investment Type [Member] Successor Ambac [Member]	Jun. 30, 2013 Asset-backed Securities [Member] Investment Type [Member] Successor Ambac [Member]	Apr. 30, 2013 Asset-backed Securities [Member] Investment Type [Member] Predecessor [Member]	Dec. 31, 2012 Asset-backed Securities [Member] Investment Type [Member] Predecessor [Member]	Sep. 30, 2014 US Government Agencies Debt Securities [Member] Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2013 US Government Agencies Debt Securities [Member] Investment Type [Member] Successor Ambac [Member]	Apr. 30, 2013 US Government Agencies Debt Securities [Member] Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2013 US Government Agencies Debt Securities [Member] Investment Type [Member] Successor Ambac [Member]	Sep. 30, 2014 US Government Agencies Debt Securities [Member] Investment Type [Member] Successor Ambac [Member]	Jun. 30, 2014 US Government Agencies Debt Securities [Member] Investment Type [Member] Successor Ambac [Member]	Dec. 31, 2013 US Government Agencies Debt Securities [Member] Investment Type [Member] Successor Ambac [Member]	Jun. 30, 2013 US Government Agencies Debt Securities [Member] Investment Type [Member] Successor Ambac [Member]	Apr. 30, 2013 US Government Agencies Debt Securities [Member] Investment Type [Member] Predecessor [Member]	Dec. 31, 2012 US Government Agencies Debt Securities [Member] Investment Type [Member] Predecessor [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability									$ (62,660)	$ (71,071)		$ (71,071)	$ (62,660)	$ (66,352)	$ (67,783)	$ (68,572)	$ (69,412)	$ (60,402)	$ (3,745)	$ (3,433)		$ (3,433)	$ (3,745)	$ (3,751)	$ (3,502)	$ (3,421)	$ (3,681)	$ (3,656)		$ 0		$ 0			$ 0	$ (3,415)	$ (3,949)	$ (6,482)	$ (215,902)	$ (305,674)	$ (305,674)	$ (215,902)	$ (218,661)	$ (186,934)	$ (340,663)	$ (415,360)	$ (415,360)	$ (322,337)	$ (133,072)	$ (103,021)	$ (103,021)	$ (133,072)	$ (129,010)	$ (92,612)	$ (108,396)	$ (137,947)	$ (137,947)	$ (108,752)	$ (82,830)	$ (202,653)	$ (202,653)	$ (82,830)	$ (89,651)	$ (94,322)	$ (232,267)	$ (277,413)	$ (277,413)	$ (213,585)	$ (58,915)	$ (67,365)		$ (67,365)	$ (58,915)	$ (62,601)	$ (64,073)	$ (61,736)	$ (61,782)	$ (50,264)		$ (273)		$ (273)			$ (208)	$ 0	$ 0	$ 0
Notional outstanding	1,958,926	2,776,103	1,958,926	2,776,103	669,251	1,337,737	1,230,874	1,291,371
Weighted average reference obligation price					$ 98.8	$ 98.0	$ 88.6	$ 85.7
Weighted average life (WAL) in years					1 year 9 months	2 years 1 month 6 days	4 years 9 months	5 years 4 months 24 days
Weighted average credit rating					AA	AA	BBB	BBB-
Weighted average relative change ratio					35.70%	35.30%	43.70%	43.10%
CVA percentage					5.63%	13.67%	16.77%	30.70%
Fair value of derivative liabilities					2,726	7,993	78,246	84,780
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings									(835)	(467)		(863)	(1,676)				33		24	23		38	72				27			(7)		(25)	0				6		3,885	37,126	107,253	(36,323)					(88,546)		(3,532)	5,931	24,838	(49,903)					(28,162)		7,417	31,195	82,415	13,580					(60,384)		(859)	(483)		(876)	(1,748)				0										0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss									254	(5,951)		(6,013)	595				(12,329)		(18)	(35)		210	(315)				(52)			7		19	0				(160)			0	0	0					0			0	0	0					0			0	0	0					0		272	(5,923)		(6,242)	910				(12,117)										0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases																	0										0										0			0	0	0					0			0	0	0					0			0	0	0					0										0										0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues												0					0										0										0			0	0	0					0			0	0	0					0			0	0	0					0										0										0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales									(3,388)				(3,388)				0										0										0			0	0	0					0			0	0	0					0			0	0	0					0		(3,388)			0	(3,388)				0					0					0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements									(885)	(4,192)		(5,490)	(2,608)				3,286										0			(3,415)		(3,955)	0				2,687		(1,126)	(2,137)	2,433	7,355					(4,477)		(530)	(556)	10,088	9,443					(1,033)		(596)	(1,581)	(7,655)	(2,088)					(3,444)			(777)		(1,535)	(2,608)				599			0			0				0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three										(273)		(273)	0				0										0										0			0	0	0					0			0	0	0					0			0	0	0					0										0			(273)		(273)					0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three												0	(208)				0										0										0			0	0	0					0			0	0	0					0			0	0	0					0										0						(208)				0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held																																							$ 3,229	$ 32,984	$ 65,509	$ (39,830)					$ (92,002)		$ (3,532)	$ 5,931	$ 24,838	$ (49,903)					$ (28,162)		$ 6,761	$ 27,053	$ 40,671	$ 10,073					$ (63,840)