v3.26.1
Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale $ 216,654 $ 268,737
Derivative assets 63 0
Derivative liabilities 0 8
Equity Securities Excluded From Fair Value Table 17,517 17,517
Commercial Mortgage Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 4,848 3,341
Short-term Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 82,513 146,442
Asset-backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 1,386 1,795
Collateralized Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 1,368 1,975
Residential Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 2,428 1,597
US Government Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 40,816 35,424
Corporate Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 73,204 66,573
Municipal Bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 10,091 11,590
Collateralized Mortgage Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 4,848 3,341
Total Fair Value [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash 79,096 68,440
Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash 79,096 68,440
Total financial assets 320,828 362,148
Long-term debt 155,486 118,901
Total financial liabilities 155,486 118,909
Reported Value Measurement [Member] | Short-term Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Short term investments 82,513 146,442
Reported Value Measurement [Member] | Other Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other investments 25,015 24,971
Reported Value Measurement [Member] | Foreign Exchange Future    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liabilities 0 8
Reported Value Measurement [Member] | Foreign Exchange Forward    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets 63 0
Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash 79,096 68,440
Total financial assets 202,425 250,306
Long-term debt 0 0
Total financial liabilities 0 0
Level 1 [Member] | Short-term Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Short term investments 82,513 146,442
Level 1 [Member] | Other Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other investments 0 0
Level 1 [Member] | Foreign Exchange Future    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liabilities 0 0
Level 1 [Member] | Foreign Exchange Forward    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets 0 0
Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash 0 0
Total financial assets 93,388 86,871
Long-term debt 0 0
Total financial liabilities 0 8
Level 2 [Member] | Short-term Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Short term investments 0 0
Level 2 [Member] | Other Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other investments 0 0
Level 2 [Member] | Foreign Exchange Future    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liabilities 0 8
Level 2 [Member] | Foreign Exchange Forward    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets 63 0
Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash 0 0
Total financial assets 0 0
Long-term debt 158,527 121,343
Total financial liabilities 158,527 121,343
Level 3 [Member] | Short-term Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Short term investments 0 0
Level 3 [Member] | Other Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other investments 0 0
Level 3 [Member] | Foreign Exchange Future    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liabilities 0 0
Level 3 [Member] | Foreign Exchange Forward    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets 0 0
Fair Value Measured at Net Asset Value Per Share [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other investments 7,498 7,454
Commercial Mortgage Backed Securities [Member] | Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 4,848 3,341
Municipal Bonds [Member] | Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 10,091 11,590
Corporate Debt Securities [Member] | Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 73,204 66,573
US Government Debt Securities [Member] | Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 40,816 35,424
Residential Mortgage-Backed Securities [Member] | Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 2,428 1,597
Collateralized Debt Obligations [Member] | Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 1,368 1,975
Asset-backed Securities [Member] | Reported Value Measurement [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 1,386 1,795
Fair Value, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 303,311 344,631
Long-term debt 158,527 121,343
Total financial liabilities 158,527 121,351
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 4,848 3,341
Fair Value, Recurring [Member] | Short-term Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Short term investments 82,513 146,442
Fair Value, Recurring [Member] | Other Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other investments 7,498 7,454
Fair Value, Recurring [Member] | Asset-backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 1,386 1,795
Fair Value, Recurring [Member] | Collateralized Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 1,368 1,975
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 2,428 1,597
Fair Value, Recurring [Member] | US Government Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 40,816 35,424
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 73,204 66,573
Fair Value, Recurring [Member] | Municipal Bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 10,091 11,590
Fair Value, Recurring [Member] | Foreign Exchange Future    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liabilities 0 8
Fair Value, Recurring [Member] | Foreign Exchange Forward    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets 63 0
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial Mortgage Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 1 [Member] | Asset-backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 1 [Member] | Collateralized Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 1 [Member] | Residential Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 1 [Member] | US Government Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 40,816 35,424
Fair Value, Recurring [Member] | Level 1 [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 1 [Member] | Municipal Bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 2 [Member] | Commercial Mortgage Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 4,848 3,341
Fair Value, Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 1,386 1,795
Fair Value, Recurring [Member] | Level 2 [Member] | Collateralized Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 1,368 1,975
Fair Value, Recurring [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 2,428 1,597
Fair Value, Recurring [Member] | Level 2 [Member] | US Government Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 2 [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 73,204 66,573
Fair Value, Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 10,091 11,590
Fair Value, Recurring [Member] | Level 3 [Member] | Commercial Mortgage Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 3 [Member] | Collateralized Debt Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 3 [Member] | Residential Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 3 [Member] | US Government Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 3 [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale 0 0
Fair Value, Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-Sale $ 0 $ 0