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Insurance Regulatory Restrictions Additional Details (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Average Annual Rate Of Return | 9.52% | 7.63%
Prescribed Discount Rate Percentage | 5.10% |
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 | 699,614 | $ 976,477
Ambac Assurance [Member] | Prescribed Or Permitted Additional Accounting Practices [Member] |  |
Statutory Accounting Practices, Prescribed Practice, Amount | (104,097) | $ 17,290
Post Rehabilitation [Member] |  |
Statutory Accounting Practices, Statutory Capital and Surplus Required | $ 100,000 |

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