Subsequent Events 2018 Balance Sheet Impact (Details) - Subsequent Event [Member] - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Feb. 12, 2018
Second Amended Plan of Rehab 2018 Expected Cash Outflow Impact	$ 1,353,560
Secured Notes Received by Ambac LSNI and Ambac Assurance		$ 768,464
Ambac Assurance Corporation [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Interest Rate on Ambac Note	5.00%
Ambac Assurance Corporation [Member] \| Minimum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Interest Rate on Ambac Note	1.00%
Ambac [Member] \| Ambac Assurance Corporation [Member]
Debt Instrument, Maturity Date	Feb. 12, 2023
Tier 2 Notes [Member] \| Ambac Assurance Corporation [Member]
Debt Instrument, Maturity Date	Feb. 12, 2055
Debt Instrument, Interest Rate, Stated Percentage	8.50%
Redemption Price After 12/17/2020 Including Principal and Interest	100.00%
Tier 2 Notes [Member] \| Ambac Assurance Corporation [Member] \| Minimum [Member]
Debt Instrument, Maturity Date	Dec. 17, 2020
Ambac Note [Domain]
Long-term debt		$ 2,154,351

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