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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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