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Municipal Bond Guarantee - Narrative (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 31, 2020 USD ($) | Apr. 30, 2018 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2018 USD ($) | Mar. 31, 2018 yr | Jun. 30, 2020 USD ($) Contract | Jun. 30, 2019 USD ($) | Dec. 31, 2019 USD ($) Contract | Dec. 31, 2018 USD ($) | Dec. 31, 2012 USD ($) | Dec. 31, 2024 | Dec. 31, 2020 | Sep. 30, 2019 USD ($) | Dec. 31, 2017 USD ($) | Jul. 31, 2012 USD ($)
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  | 50.00% |  |  | 53.80% |  | 50.00% |  |  |  |  |  |  |
Percent change in discounted future cash flows |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  | $ 1.1 | $ 21.7 |  |  |  |  |  |  |  |
Interest paid |  |  |  |  |  | $ 6.7 | $ 7.3 |  |  |  |  |  |  |  |
HG Global |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Partners capital contribution |  |  |  |  |  |  |  |  |  | $ 594.5 |  |  |  |  |
Surplus notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 503.0
Cash and Fixed Income Securities |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.0
Percent over a target trust balance |  |  |  |  |  | 102.00% |  |  |  |  |  |  |  |  |
Supplement Trust Target |  |  |  |  |  | $ 603.0 |  |  |  |  |  |  |  |  |
HG Global | Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  | 96.90% |  | 96.60% |  |  |  |  |  |  |
HG Global | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  | 88.40% |  |  | 88.40% |  | 89.60% |  |  |  |  |  |  |
BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of risk premium ceded |  |  | 60.00% |  |  |  |  |  |  |  |  |  |  |  |
Number of years of change in interest rate |  |  |  |  |  |  |  |  | 3 |  |  |  |  |  |
Year of U.S. Treasury rate | yr |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |
Contracts outstanding | Contract |  |  |  |  |  | 9,992 |  | 8,987 |  |  |  |  |  |  |
Remaining weighted average contract period outstanding (in years) |  |  |  |  |  | 10 years 7 months 6 days |  | 10 years 8 months 12 days |  |  |  |  |  |  |
Municipal bond outstanding principal |  |  |  |  |  | $ 67,591.5 |  | $ 62,250.5 |  |  |  |  | $ 1,100.0 |  |
Municipal bond outstanding interest |  |  |  |  |  | 33,775.8 |  | 31,799.7 |  |  |  |  |  |  |
Municipal bond debt service outstanding |  |  |  |  |  | 101,367.3 |  | 94,050.2 |  |  |  |  |  |  |
April 1, 2020 - December 31, 2020 |  |  |  |  |  | 10.2 |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  | 19.6 |  |  |  |  |  |  |  |  |
2022 |  |  |  |  |  | 18.5 |  |  |  |  |  |  |  |  |
2023 |  |  |  |  |  | 17.3 |  |  |  |  |  |  |  |  |
2024 |  |  |  |  |  | 16.2 |  |  |  |  |  |  |  |  |
2025 |  |  |  |  |  | 15.0 |  |  |  |  |  |  |  |  |
2026 and thereafter |  |  |  |  |  | 121.8 |  |  |  |  |  |  |  |  |
Total gross unearned insurance premiums |  |  |  |  |  | 218.6 |  | 198.4 |  |  |  |  |  |  |
HG Global |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collateral held in supplement trust |  |  |  |  |  | 811.8 |  | 786.7 |  |  |  |  |  |  |
Interest receivable |  |  |  |  |  | $ 155.0 |  | 162.7 |  |  |  |  |  |  |
HG Re |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of par value of policy reinsured |  |  |  |  |  | 15.00% |  |  |  |  |  |  |  |  |
BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Surplus notes |  |  |  |  |  | $ 409.7 |  | 457.6 |  |  |  |  |  |  |
Interest receivable |  |  |  |  |  | $ 4.7 |  | $ 7.5 |  |  |  |  |  |  |
BAM Management |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Partners capital contribution |  |  |  |  |  |  |  |  |  | $ 14.5 |  |  |  |  |
Supplemental Trust [Member] | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  | $ 47.9 |  |  |  |  |  |  |  |  |  |  |  |
Accrued Interest Payment on Surplus Notes |  |  | 0.9 |  |  |  |  |  |  |  |  |  |  |  |
Surplus Note | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, fixed interest rate (as a percent) |  |  |  |  |  |  |  | 5.70% |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  | 65.0 |  |  |  |  |  |  |  |  |  |  |  |
Accrued Interest Payment on Surplus Notes |  |  | $ 16.2 |  |  |  |  |  |  |  |  |  |  |  |
Combination One | Surplus Note | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of years of change in interest rate | yr |  |  |  |  | 5 |  |  |  |  |  |  |  |  |  |
US Treasury Rate | Surplus Note | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  | 3.00% |  |  |  |  |  |  |  |  |
Fixed interest rate | Surplus Note | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, fixed interest rate (as a percent) |  |  |  | 8.00% |  |  |  |  | 8.00% |  |  |  |  |  |
First Quarter, year two | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  | $ 5.0 |  |  |  |  |  |  |  |  |
Second Quarter, year two | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  | 4.9 |  |  |  |  |  |  |  |  |
Third Quarter, year two | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  | 4.9 |  |  |  |  |  |  |  |  |
Fourth Quarter, year two | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2021 |  |  |  |  |  | $ 4.8 |  |  |  |  |  |  |  |  |
Series A BAM Surplus Note | HG Global |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Surplus notes |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 203.0 | 203.0
Series B BAM Surplus Note | HG Global |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Surplus notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 300.0
BAM | Fidus Re Ltd. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Losses above retention, percentage of liability |  | 90.00% |  |  |  |  |  |  |  |  |  |  |  |  |
BAM | HG Global |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of Agreement | 10 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fidus Re Ltd. | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Secured Debt |  | $ 100.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal bond outstanding principal |  |  |  | $ 2,200.0 |  |  |  |  | $ 2,200.0 |  |  |  |  |  |
Collateralized financial guarantee, term |  | 12 years |  |  |  |  |  |  |  |  |  |  |  |  |
Collateral financial guarantee, callable term |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |
Aggregate losses on ceded business |  | $ 165.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Premium receivable, Premium expected to be collected |  | 100.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of Quota Share Reinsurance Agreement |  |  |  | 100.00% |  |  |  |  |  |  |  |  |  |  |
Maximum | BAM | HG Global |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate losses on ceded business | $ 75.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum | Fidus Re Ltd. | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate losses on ceded business |  | $ 276.1 |  |  |  |  |  |  |  |  |  |  |  |  |
Scenario, Forecast | Surplus Note | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, fixed interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 4.60% |  |  |
Scenario, Forecast | Fixed interest rate | Surplus Note | BAM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, fixed interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  | 8.00% |  |  |  |

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