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Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Mar. 31, 2023
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value $ 2,095,000    
Debt Securities, Available-for-sale, Allowance for Credit Loss 2,000 $ 3,000 $ 1,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 37,000 40,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 75,000 71,000  
Financial assets:      
Derivative assets 21,000 26,000  
Other assets 0    
Long-term Debt 512,000 508,000  
Financial liabilities:      
Derivative liabilities 29,000 35,000  
Equity Securities Excluded From Fair Value Table 13,000 13,000  
Debt Securities, Available-for-sale, Amortized Cost 2,135,000 2,197,000  
Debt Securities, Available-for-Sale, Current 2,095,000 2,162,000  
Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 1,687,000 1,710,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 2,000 3,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 37,000 40,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 74,000 71,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 1,726,000 1,744,000  
Fixed Income Investments And Other Investments [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 2,068,000 2,135,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 2,000 3,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 37,000 40,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 74,000 71,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 2,108,000 2,170,000  
Commercial Mortgage Backed Securities [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 27,000    
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 0 0  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 27,000    
Short-term Investments [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 382,000 426,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 0 0  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 382,000 426,000  
Asset-backed Securities [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 231,000 303,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 3,000 3,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 5,000 1,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 232,000 301,000  
Collateralized Debt Obligations [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 143,000 139,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 1,000 1,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 0 1,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 143,000 139,000  
Residential Mortgage-Backed Securities [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 253,000 250,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 2,000 3,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 28,000 28,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 12,000 14,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 239,000 239,000  
US Government Debt Securities [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 98,000 82,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 0 1,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 4,000 4,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 101,000 85,000  
Debt Security, Government, Non-US [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 99,000 100,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 1,000 1,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 7,000 6,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 105,000 105,000  
Corporate Debt Securities [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 765,000 745,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 3,000 4,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 45,000 44,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 807,000 785,000  
Municipal Bonds [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 72,000 72,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 1,000 1,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 1,000 1,000  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 72,000 72,000  
Collateralized Mortgage Backed Securities [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 27,000 19,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 0 0  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 27,000 19,000  
Total Fair Value [Member]      
Financial assets:      
Cash 44,000 28,000  
Reported Value Measurement [Member]      
Financial assets:      
Other investments 152,000 77,000  
Cash 44,000 28,000  
Loans 2,000 2,000  
Total financial assets 6,987,000 7,022,000  
Financial liabilities:      
Liabilities for net financial guarantees written 231,000 292,000  
Long-term debt 999,000 983,000  
Total financial liabilities 5,354,000 5,474,000  
Reported Value Measurement [Member] | Short-term Investments [Member]      
Financial assets:      
Short term investments 382,000 426,000  
Reported Value Measurement [Member] | Other Debt Obligations [Member]      
Financial assets:      
Other investments 558,000 475,000  
Reported Value Measurement [Member] | Interest Rate Swap [Member]      
Financial liabilities:      
Derivative liabilities 29,000 35,000  
Reported Value Measurement [Member] | Interest Rate Swap [Member] | Other Assets [Member]      
Financial assets:      
Derivative assets 21,000 25,000  
Reported Value Measurement [Member] | Warrants [Member]      
Financial assets:      
Derivative assets 1,000 1,000  
Level 1 [Member]      
Financial assets:      
Cash 44,000 27,000  
Total financial assets 1,049,000 979,000  
Financial liabilities:      
Liabilities for net financial guarantees written 0 0  
Long-term debt 0 0  
Total financial liabilities 0 0  
Level 1 [Member] | Short-term Investments [Member]      
Financial assets:      
Short term investments 379,000 421,000  
Level 1 [Member] | Loans Receivable [Member]      
Financial assets:      
Loans 0 0  
Level 1 [Member] | Other Debt Obligations [Member]      
Financial assets:      
Other investments 152,000 77,000  
Level 1 [Member] | Interest Rate Swap [Member]      
Financial liabilities:      
Derivative liabilities 0 0  
Level 1 [Member] | Interest Rate Swap [Member] | Other Assets [Member]      
Financial assets:      
Derivative assets 0 0  
Level 1 [Member] | Warrants [Member]      
Financial assets:      
Derivative assets 0 0  
Level 2 [Member]      
Financial assets:      
Cash 0 2,000  
Total financial assets 1,747,000 1,795,000  
Financial liabilities:      
Liabilities for net financial guarantees written 0 0  
Long-term debt 753,000 679,000  
Total financial liabilities 4,670,000 4,671,000  
Level 2 [Member] | Short-term Investments [Member]      
Financial assets:      
Short term investments 2,000 5,000  
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] | Interest Rate Swap [Member]      
Financial liabilities:      
Derivative liabilities 29,000 35,000  
Level 2 [Member] | Interest Rate Swap [Member] | Other Assets [Member]      
Financial assets:      
Derivative assets 0 0  
Level 2 [Member] | Warrants [Member]      
Financial assets:      
Derivative assets 0 0  
Level 3 [Member]      
Financial assets:      
Cash 0 0  
Total financial assets 3,783,000 3,850,000  
Financial liabilities:      
Liabilities for net financial guarantees written 498,000 788,000  
Long-term debt 19,000 18,000  
Total financial liabilities 718,000 1,026,000  
Level 3 [Member] | Short-term Investments [Member]      
Financial assets:      
Short term investments 0 0  
Level 3 [Member] | Loans Receivable [Member]      
Financial assets:      
Loans 2,000 2,000  
Level 3 [Member] | Other Debt Obligations [Member]      
Financial assets:      
Other investments 0 0  
Level 3 [Member] | Interest Rate Swap [Member]      
Financial liabilities:      
Derivative liabilities 0 0  
Level 3 [Member] | Interest Rate Swap [Member] | Other Assets [Member]      
Financial assets:      
Derivative assets 21,000 25,000  
Level 3 [Member] | Warrants [Member]      
Financial assets:      
Derivative assets 1,000 1,000  
Commercial Mortgage Backed Securities [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 27,000 19,000  
Municipal Bonds [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 101,000 99,000  
Corporate Debt Securities [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 765,000 745,000  
Debt Security, Government, Non-US [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 99,000 100,000  
US Government Debt Securities [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 98,000 82,000  
Residential Mortgage-Backed Securities [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 253,000 250,000  
Collateralized Debt Obligations [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 143,000 139,000  
Asset-backed Securities [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 231,000 303,000  
Fair Value, Recurring [Member]      
Financial assets:      
Total financial assets 6,974,000 7,010,000  
Financial liabilities:      
Liabilities for net financial guarantees written 498,000 788,000  
Long-term debt 772,000 697,000  
Total financial liabilities 5,388,000 5,697,000  
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 27,000 19,000  
Fair Value, Recurring [Member] | Short-term Investments [Member]      
Financial assets:      
Short term investments 382,000 426,000  
Fair Value, Recurring [Member] | Loans Receivable [Member]      
Financial assets:      
Loans 2,000 2,000  
Fair Value, Recurring [Member] | Other Debt Obligations [Member]      
Financial assets:      
Other investments 546,000 463,000  
Fair Value, Recurring [Member] | Asset-backed Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 231,000 303,000  
Fair Value, Recurring [Member] | Collateralized Debt Obligations [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 143,000 139,000  
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 253,000 250,000  
Fair Value, Recurring [Member] | US Government Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 98,000 82,000  
Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 99,000 100,000  
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 765,000 745,000  
Fair Value, Recurring [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 101,000 99,000  
Fair Value, Recurring [Member] | Interest Rate Swap [Member]      
Financial liabilities:      
Derivative liabilities 29,000 35,000  
Fair Value, Recurring [Member] | Interest Rate Swap [Member] | Other Assets [Member]      
Financial assets:      
Derivative assets 21,000 25,000  
Fair Value, Recurring [Member] | Warrants [Member]      
Financial assets:      
Derivative assets 1,000 1,000  
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]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 98,000 82,000  
Fair Value, Recurring [Member] | Level 1 [Member] | Debt Security, Government, Non-US [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 99,000 100,000  
Fair Value, Recurring [Member] | Level 1 [Member] | Corporate Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 27,000 19,000  
Fair Value, Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 163,000 235,000  
Fair Value, Recurring [Member] | Level 2 [Member] | Collateralized Debt Obligations [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 143,000 139,000  
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]      
Fixed maturity securities, at fair value 253,000 250,000  
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]      
Fixed maturity securities, at fair value 0 0  
Fair Value, Recurring [Member] | Level 2 [Member] | Debt Security, Government, Non-US [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 746,000 726,000  
Fair Value, Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 101,000 99,000  
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]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 68,000 68,000  
Fair Value, Recurring [Member] | Level 3 [Member] | Collateralized Debt Obligations [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 0 0  
Fair Value, Recurring [Member] | Level 3 [Member] | Debt Security, Government, Non-US [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 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]      
Fixed maturity securities, at fair value 19,000 19,000  
Fair Value, Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 0  
Collateral Pledged [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 26,000 27,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 1,000 0  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 27,000 0  
Collateral Pledged [Member] | Short-term Investments [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 27,000  
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 0 0  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 0 0  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 0 27,000  
Collateral Pledged [Member] | US Government Debt Securities [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 26,000 0  
Collateral Pledged [Member] | Short-term Investments [Member] | Reported Value Measurement [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 27,000  
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Short-term Investments [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 27,000  
Collateral Pledged [Member] | Fair Value, Recurring [Member] | US Government Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 26,000 0  
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 1 [Member] | Short-term Investments [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 27,000  
Collateral Pledged [Member] | 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]      
Fixed maturity securities, at fair value 26,000 0  
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 2 [Member] | Short-term Investments [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 0  
Collateral Pledged [Member] | 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]      
Fixed maturity securities, at fair value 0 0  
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 3 [Member] | Short-term Investments [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 0  
Collateral Pledged [Member] | 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]      
Fixed maturity securities, at fair value 0 0  
Asset Pledged as Collateral [Member] | Fixed Income Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Debt Securities, Available-for-sale, Allowance for Credit Loss 0 0  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 27,000 27,000  
Variable Interest Entity, Primary Beneficiary [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 2,162,000 2,167,000  
Financial assets:      
Loans 1,604,000 1,663,000  
Derivative assets 221,000 226,000  
Long-term Debt 2,925,000 2,967,000  
Financial liabilities:      
Derivative liabilities 1,170,000 1,197,000  
Long-term debt 2,671,000 2,710,000  
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 2,070,000 2,072,000  
Variable Interest Entity, Primary Beneficiary [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 92,000 95,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 7,000 7,000  
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 0 0  
Financial liabilities:      
Debt Securities, Available-for-sale, Amortized Cost 85,000 88,000  
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member]      
Financial assets:      
Restricted Cash and Cash Equivalents, Current 252,000 246,000  
Loans 1,604,000 1,663,000  
Financial liabilities:      
Long-term debt 2,925,000 2,967,000  
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member] | Corporate Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 2,070,000 2,072,000  
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 92,000   $ 95,000
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member] | Interest Rate Swap [Member]      
Financial assets:      
Derivative assets 186,000 190,000  
Financial liabilities:      
Derivative liabilities 1,170,000 1,197,000  
Variable Interest Entity, Primary Beneficiary [Member] | Reported Value Measurement [Member] | Currency Swaps [Member]      
Financial assets:      
Derivative assets 35,000 36,000  
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member]      
Financial assets:      
Restricted Cash and Cash Equivalents, Current 252,000 246,000  
Loans 0 0  
Financial liabilities:      
Long-term debt 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member] | Corporate Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member] | Interest Rate Swap [Member]      
Financial assets:      
Derivative assets 0 0  
Financial liabilities:      
Derivative liabilities 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Level 1 [Member] | Currency Swaps [Member]      
Financial assets:      
Derivative assets 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member]      
Financial assets:      
Restricted Cash and Cash Equivalents, Current 0  
Loans 0 0  
Financial liabilities:      
Long-term debt 2,718,000 2,760,000  
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member] | Corporate Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 92,000 95,000  
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member] | Interest Rate Swap [Member]      
Financial assets:      
Derivative assets 186,000 190,000  
Financial liabilities:      
Derivative liabilities 1,170,000 1,197,000  
Variable Interest Entity, Primary Beneficiary [Member] | Level 2 [Member] | Currency Swaps [Member]      
Financial assets:      
Derivative assets 35,000 36,000  
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member]      
Financial assets:      
Restricted Cash and Cash Equivalents, Current 0 0  
Loans 1,604,000 1,663,000  
Financial liabilities:      
Long-term debt 202,000 220,000  
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Corporate Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 2,070,000 2,072,000  
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Interest Rate Swap [Member]      
Financial assets:      
Derivative assets 0 0  
Financial liabilities:      
Derivative liabilities 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Level 3 [Member] | Currency Swaps [Member]      
Financial assets:      
Derivative assets 0 0  
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member]      
Financial assets:      
Restricted Cash and Cash Equivalents, Current 252,000 246,000  
Loans 1,604,000 1,663,000  
Financial liabilities:      
Long-term debt 2,920,000 2,980,000  
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member] | Corporate Debt Securities [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 2,070,000 2,072,000  
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member] | Municipal Bonds [Member]      
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]      
Fixed maturity securities, at fair value 92,000 95,000  
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member] | Interest Rate Swap [Member]      
Financial assets:      
Derivative assets 186,000 190,000  
Financial liabilities:      
Derivative liabilities 1,170,000 1,197,000  
Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Recurring [Member] | Currency Swaps [Member]      
Financial assets:      
Derivative assets $ 35,000 $ 36,000