Long-Term Debt (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Jul. 31, 2015	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	May 01, 2013	May 19, 2011
Debt Instrument [Line Items]
Secured Debt		$ 102,403				$ 130,571				$ 102,403	$ 130,571
Junior surplus note of Ambac Assurance Segregated Account													$ 350,000
Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 102,986				132,467				$ 102,986	132,467
5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		10.50%								10.50%
Debt Instrument, Repurchased Face Amount		$ 18,551				11,804				$ 18,551	11,804
Net realized gains (losses) on extinguishment of debt										1,677	(1,246)	$ 71,590
Debt Instrument, Face Amount		$ 862,945				881,496				$ 862,945	881,496
5.1% Surplus Notes, Segregated Account, Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		10.50%								10.50%
Net realized gains (losses) on extinguishment of debt												3,134
Debt Instrument, Face Amount		$ 39,102				39,102				$ 39,102	39,102
5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		19.50%								19.50%
Debt Instrument, Face Amount		$ 374,036				378,039				$ 374,036	378,039
One State Street [Member] | 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument Principal Amount Subject To Repurchase														$ 13,056
Debt Instrument, Face Amount		$ 24,037				28,039				24,037	28,039
Extinguishment of Debt, Amount										$ 4,002
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member] | 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		8.40%								8.40%
Successor [Member]
Debt Instrument [Line Items]
Long-term debt		$ 1,114,405				1,124,950				$ 1,114,405	1,124,950
Net realized gains (losses) on extinguishment of debt		0	$ 24	$ 3,586	$ 1,235	0	$ 1,420	$ (1,246)	$ (93)	4,845	81	$ (74,724)
Successor [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Long-term debt		1,114,405				1,124,950				1,114,405	1,124,950
Secured Debt		102,403				130,571				102,403	130,571
Successor [Member] | Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, General Account, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt		730,648				715,211				730,648	715,211
Successor [Member] | Ambac Assurance Corporation [Member] | 5.1% Surplus Notes, Segregated Account, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt		33,107				31,725				33,107	31,725
Successor [Member] | Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt		248,247				247,443				248,247	247,443
Successor [Member] | Variable Interest Entities [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage												6.65%
Long-term debt		11,155,936				$ 12,327,960				11,155,936	$ 12,327,960
Successor [Member] | 5.1% Surplus Notes, General Account, Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						5.10%					5.10%	5.10%
Debt Instruments Maturity Year											2020	2020
Successor [Member] | 5.1% Surplus Notes, Segregated Account, Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						5.10%					5.10%	5.10%
Debt Instruments Maturity Year											2020	2020
Successor [Member] | 5.1% Junior Surplus Notes, Segregated Account Due 2020 [Member] | Ambac Assurance Corporation [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						5.10%					5.10%	5.10%
Debt Instruments Maturity Year											2020	2020
Consolidated Variable Interest Entities [Member]
Debt Instrument [Line Items]
Unpaid Principal Amount Of Fixed Rate Debt Accounted For Under Fair Value Option		8,854,530				$ 10,803,729				8,854,530	$ 10,803,729
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months		0								0
Long-term Debt, Maturities, Repayments of Principal in Year Two		128,801								128,801
Long-term Debt, Maturities, Repayments of Principal in Year Three		301,375								301,375
Long-term Debt, Maturities, Repayments of Principal in Year Four		46,848								46,848
Long-term Debt, Maturities, Repayments of Principal in Year Five		$ 107,432								$ 107,432
Consolidated Variable Interest Entities [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		0.82%				0.96%				0.82%	0.96%
Consolidated Variable Interest Entities [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		13.00%				13.00%				13.00%	13.00%
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest Rate on Securities Issued by Delaware Trust	2.80%