v3.26.1
Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands
Apr. 01, 2026
Mar. 31, 2026
Dec. 31, 2025
Oct. 31, 2025
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   $ 229,387 $ 268,737  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   596 1,205  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   2,746 2,316  
Financial assets:        
Derivative assets   3 0  
Short-Term Debt   0 0  
Long-term Debt $ 139,375 117,062 117,558 $ 100,000
Financial liabilities:        
Derivative liabilities   429 8  
Equity Securities Excluded From Fair Value Table   17,517 17,517  
Debt Securities, Available-for-sale, Amortized Cost   231,537 269,848  
Debt Securities, Available-for-Sale, Current   229,387 268,737  
Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   137,092 122,295  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   596 1,197  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   2,746 2,316  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   139,242 123,414  
Fixed Income Investments And Other Investments [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   2,746    
Commercial Mortgage Backed Securities [Member] | Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   4,985 3,341  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   40 8  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   5,002 3,307  
Short-term Investments [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   92,295 146,442  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   0 8  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   0 0  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   92,295 146,434  
Asset-backed Securities [Member] | Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   1,392 1,795  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   12 23  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   0 0  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   1,380 1,772  
Collateralized Debt Obligations [Member] | Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   1,630 1,975  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   5 12  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   1 0  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   1,626 1,963  
Residential Mortgage-Backed Securities [Member] | Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   2,627 1,597  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   5 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   21 7  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   2,643 1,604  
US Government Debt Securities [Member] | Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   39,042 35,424  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   166 365  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   218 131  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   39,094 35,190  
Corporate Debt Securities [Member] | Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   76,940 66,573  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   298 634  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   2,249 1,942  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   78,891 67,881  
Municipal Bonds [Member] | Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   10,476 11,590  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   87 121  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   217 228  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   10,606 11,697  
Collateralized Mortgage Backed Securities [Member] | Fixed Income Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   4,985 3,341  
Debt Securities, Available-for-sale, Allowance for Credit Loss   0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax   23 42  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax   40 8  
Financial liabilities:        
Debt Securities, Available-for-sale, Amortized Cost   5,002 3,307  
Total Fair Value [Member]        
Financial assets:        
Cash   93,537 68,440  
Reported Value Measurement [Member]        
Financial assets:        
Cash   93,537 68,440  
Loans   0 0  
Total financial assets   347,895 362,148  
Short-Term Debt   0 0  
Financial liabilities:        
Long-term debt   118,367 118,901  
Total financial liabilities   118,793 118,909  
Reported Value Measurement [Member] | Short-term Investments [Member]        
Financial assets:        
Short term investments   92,295 146,442  
Reported Value Measurement [Member] | Other Debt Obligations [Member]        
Financial assets:        
Other investments   24,971 24,971  
Reported Value Measurement [Member] | Foreign Exchange Future        
Financial liabilities:        
Derivative liabilities   426 8  
Reported Value Measurement [Member] | Foreign Exchange Forward        
Financial assets:        
Derivative assets   0 0  
Level 1 [Member]        
Financial assets:        
Cash   93,537 68,440  
Total financial assets   224,874 250,306  
Short-Term Debt   0 0  
Financial liabilities:        
Long-term debt   0 0  
Total financial liabilities   0 0  
Level 1 [Member] | Short-term Investments [Member]        
Financial assets:        
Short term investments   92,295 146,442  
Level 1 [Member] | Loans Receivable [Member]        
Financial assets:        
Loans   0 0  
Level 1 [Member] | Other Debt Obligations [Member]        
Financial assets:        
Other investments   0 0  
Level 1 [Member] | Foreign Exchange Future        
Financial liabilities:        
Derivative liabilities   0 0  
Level 1 [Member] | Foreign Exchange Forward        
Financial assets:        
Derivative assets   0 0  
Level 2 [Member]        
Financial assets:        
Cash   0 0  
Total financial assets   98,050 86,871  
Short-Term Debt   0 0  
Financial liabilities:        
Long-term debt   0 0  
Total financial liabilities   426 8  
Level 2 [Member] | Short-term Investments [Member]        
Financial assets:        
Short term investments   0 0  
Level 2 [Member] | Loans Receivable [Member]        
Financial assets:        
Loans   0 0  
Level 2 [Member] | Other Debt Obligations [Member]        
Financial assets:        
Other investments   0 0  
Level 2 [Member] | Foreign Exchange Future        
Financial liabilities:        
Derivative liabilities   426 8  
Level 2 [Member] | Foreign Exchange Forward        
Financial assets:        
Derivative assets   0 0  
Level 3 [Member]        
Financial assets:        
Cash   0 0  
Total financial assets   0 0  
Short-Term Debt   0 0  
Financial liabilities:        
Long-term debt   118,367 121,343  
Total financial liabilities   118,367 121,343  
Level 3 [Member] | Short-term Investments [Member]        
Financial assets:        
Short term investments   0 0  
Level 3 [Member] | Loans Receivable [Member]        
Financial assets:        
Loans   0 0  
Level 3 [Member] | Other Debt Obligations [Member]        
Financial assets:        
Other investments   0 0  
Level 3 [Member] | Foreign Exchange Future        
Financial liabilities:        
Derivative liabilities   0 0  
Level 3 [Member] | Foreign Exchange Forward        
Financial assets:        
Derivative assets   0 0  
Commercial Mortgage Backed Securities [Member] | Reported Value Measurement [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   4,985 3,341  
Municipal Bonds [Member] | Reported Value Measurement [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   10,476 11,590  
Corporate Debt Securities [Member] | Reported Value Measurement [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   76,940 66,573  
US Government Debt Securities [Member] | Reported Value Measurement [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   39,042 35,424  
Residential Mortgage-Backed Securities [Member] | Reported Value Measurement [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   2,627 1,597  
Collateralized Debt Obligations [Member] | Reported Value Measurement [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   1,630 1,975  
Asset-backed Securities [Member] | Reported Value Measurement [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   1,392 1,795  
Fair Value, Recurring [Member]        
Financial assets:        
Total financial assets   330,378 344,631  
Short-Term Debt   0 0  
Financial liabilities:        
Long-term debt   118,367 121,343  
Total financial liabilities   118,793 121,351  
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   4,985 3,341  
Fair Value, Recurring [Member] | Short-term Investments [Member]        
Financial assets:        
Short term investments   92,295 146,442  
Fair Value, Recurring [Member] | Loans Receivable [Member]        
Financial assets:        
Loans   0 0  
Fair Value, Recurring [Member] | Other Debt Obligations [Member]        
Financial assets:        
Other investments   7,454 7,454  
Fair Value, Recurring [Member] | Asset-backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   1,392 1,795  
Fair Value, Recurring [Member] | Collateralized Debt Obligations [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   1,630 1,975  
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   2,627 1,597  
Fair Value, Recurring [Member] | US Government Debt Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   39,042 35,424  
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   76,940 66,573  
Fair Value, Recurring [Member] | Municipal Bonds [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   10,476 11,590  
Fair Value, Recurring [Member] | Foreign Exchange Future        
Financial liabilities:        
Derivative liabilities   426 8  
Fair Value, Recurring [Member] | Foreign Exchange Forward        
Financial assets:        
Derivative assets   0 0  
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial Mortgage Backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 1 [Member] | Asset-backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 1 [Member] | Collateralized Debt Obligations [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 1 [Member] | Residential Mortgage-Backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 1 [Member] | US Government Debt Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   39,042 35,424  
Fair Value, Recurring [Member] | Level 1 [Member] | Corporate Debt Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 1 [Member] | Municipal Bonds [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 2 [Member] | Commercial Mortgage Backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   4,985 3,341  
Fair Value, Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   1,392 1,795  
Fair Value, Recurring [Member] | Level 2 [Member] | Collateralized Debt Obligations [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   1,630 1,975  
Fair Value, Recurring [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   2,627 1,597  
Fair Value, Recurring [Member] | Level 2 [Member] | US Government Debt Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 2 [Member] | Corporate Debt Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   76,940 66,573  
Fair Value, Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   10,476 11,590  
Fair Value, Recurring [Member] | Level 3 [Member] | Commercial Mortgage Backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 3 [Member] | Collateralized Debt Obligations [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 3 [Member] | Residential Mortgage-Backed Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 3 [Member] | US Government Debt Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 3 [Member] | Corporate Debt Securities [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   0 0  
Fair Value, Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]        
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]        
Debt Securities, Available-for-Sale   $ 0 $ 0