Insurance Regulatory Restrictions Additional Details (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Average Annual Rate Of Return	5.87%	9.52%
Prescribed Discount Rate Percentage	5.10%
Statutory Accounting Practices, Statutory Capital and Surplus Required	$ 100,000
Statutory Accounting Practices, Statutory Capital and Surplus Required Pursuant to AMPS Exchange	$ 75,000
Quarterly Dividend Increase Limitation Percentage	15.00%
Percentage Of Policy Holders Surplus	10.00%
Minimum [Member]
Settlement Agreement Annual Restricted Payment Amount	$ 5,000
Maximum [Member]
Settlement Agreement Annual Restricted Payment Amount	7,500
Ambac Assurance [Member]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	1,152,346	$ 699,614
Ambac Assurance [Member] \| Prescribed Or Permitted Additional Accounting Practices [Member]
Statutory Accounting Practices, Prescribed Practice, Amount	$ (41,814)	$ (104,097)
5.1 % Surplus Notes Due 2020 [Member] \| Ambac Assurance Corporation [Member]
Debt Instrument, Interest Rate, Stated Percentage	5.10%	5.10%

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Percentage Of Policy Holders Surplus

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Discount rate percentage for the purpose of discounting statutory loss reserves and estimated impairment losses on subsidiary guarantees prescribed the regulator.

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No quarterly dividend may exceed the dividend paid in the corresponding quarter by more than this percentage without notification to the regulator.

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Settlement Agreement Annual Restricted Payment Amount

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Statutory Accounting Practices, Statutory Capital and Surplus Required Pursuant to AMPS Exchange

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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Amount as of the balance sheet date of each item listed to reconcile the differences resulting from applying state prescribed statutory accounting practices rather than statutory accounting practices prescribed by National Association of Insurance Commissioners.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
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The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
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Amount of statutory capital required to be maintained as of the balance sheet date under prescribed or permitted statutory accounting practices.

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