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Debt - Narrative (Details) £ in Millions |  |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 02, 2021 USD ($) | Jun. 01, 2021 | Apr. 07, 2020 USD ($) | Apr. 07, 2020 GBP (£) | Apr. 06, 2020 USD ($) | Mar. 31, 2007 USD ($) | Jun. 30, 2021 USD ($) credit_facility | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) credit_facility | Jun. 30, 2021 GBP (£) | Jun. 30, 2020 USD ($) | Jun. 30, 2021 EUR (€) credit_facility | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Jun. 15, 2018 USD ($) | Mar. 31, 2007 EUR (€)
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  | $ 428,800,000 |  | $ 428,800,000 |  |  |  |  | $ 376,400,000 |  |  |  |
Debt covenant, maximum loan to value percent, period one |  |  |  |  |  |  | 50.00% |  | 50.00% |  |  | 50.00% |  |  |  |  |  |
Debt covenant, maximum loan to value percent, period two |  |  |  |  |  |  | 40.00% |  | 40.00% |  |  | 40.00% |  |  |  |  |  |
Debt covenant, maximum loan to value percent, period three |  |  |  |  |  |  | 25.00% |  | 25.00% |  |  | 25.00% |  |  |  |  |  |
Debt covenant, maximum loan to value percent, period four |  |  |  |  |  |  | 15.00% |  | 15.00% |  |  | 15.00% |  |  |  |  |  |
Debt covenant, maximum loan to value percent, period five |  |  |  |  |  |  | 0.00% |  | 0.00% |  |  | 0.00% |  |  |  |  |  |
Debt covenant, maximum loan to value percent |  |  |  |  |  |  | 23.20% |  | 23.20% |  |  | 23.20% |  |  |  |  |  |
Draw down of debt and revolving line of credit |  |  |  |  |  |  |  |  | $ 105,300,000 |  | $ 69,400,000 |  |  |  |  |  |  |
Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Secured credit facilities | credit_facility |  |  |  |  |  |  | 3 |  | 3 |  |  | 3 |  |  |  |  |  |
Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  | $ 270,700,000 |  | $ 270,700,000 |  |  |  |  | 272,600,000 |  |  |  |
Specialty Insurance Distribution (NSM) | Kingsbridge Group Limited |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings |  |  | $ 52,400,000 | £ 42.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ark | Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit |  |  |  |  |  |  | 45,000,000.0 |  | 45,000,000.0 |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 150,000,000.0 |  | 150,000,000.0 |  |  |  |  |  |  |  |  |
Ark Alesco Note | Junior Notes | Ark |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount borrowed |  |  |  |  |  | $ 30,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  | 30,000,000.0 |  | 30,000,000.0 |  |  |  |  |  |  |  |  |
Ark Alesco Note | Junior Notes | USD-LIBOR | Ark |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  | 4.60% |  |  |  |  |  |  |  |  |  |  |  |
Ark Dekania Note | Junior Notes | Ark |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount borrowed | € |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | € 12,000,000.0
Debt |  |  |  |  |  |  | 14,200,000 |  | 14,200,000 |  |  | € 12,000,000.0 |  |  |  |  |  |
Ark Dekania Note | Junior Notes | EURIBOR | Ark |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  | 4.60% |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount borrowed |  |  |  |  |  |  | 276,600,000 |  | 276,600,000 |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  | 276,600,000 | $ 273,400,000 | $ 276,600,000 |  | 273,400,000 |  | $ 277,300,000 | 277,400,000 | $ 220,700,000 | $ 221,300,000 |  |
Total commitment under revolving credit facility |  |  | 291,400,000 |  | $ 234,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of discounted future cash flows |  |  |  |  |  |  |  |  | 10.00% | 10.00% |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  | 269,400,000 |  | $ 269,400,000 |  |  |  |  | 271,300,000 |  |  |  |
Outstanding balance |  |  |  |  |  |  | 276,600,000 |  | 276,600,000 |  |  |  |  | 277,400,000 |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount borrowed | $ 50,000,000.0 |  | 276,400,000 |  | $ 224,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings |  |  | $ 52,400,000 | £ 42.5 |  |  | 0 | 52,400,000 | 0 |  | 52,400,000 |  |  |  |  |  |  |
Floor rate |  |  | 1.25% | 1.25% |  |  |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | Kingsbridge Group Limited |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  | 52,400,000 |  |  | 52,400,000 |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | Interest Rate Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 151,000,000.0 |
Hedged liability, fair value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 151,000,000.0 |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | Interest Rate Swap | Term loan - hedged |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  | 146,800,000 |  | 146,800,000 |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | Interest Rate Swap | Term loan - unhedged |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  | 129,800,000 |  | 129,800,000 |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | USD-LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Floor rate |  |  | 1.25% | 1.25% |  |  |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | USD-LIBOR | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 4.50% | 5.50% | 5.50% | 5.50% | 4.25% |  |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | USD-LIBOR | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 5.00% | 6.00% | 6.00% | 6.00% | 4.75% |  |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | GBP-LIBOR | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 5.00% | 6.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | GBP-LIBOR | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 5.50% | 6.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | GBP Term Loan | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  | 58,100,000 | £ 42.1 |  |  |  |  |  |  |  |
NSM Bank Facility | Revolving credit loan | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility | $ 40,000,000.0 |  | $ 15,000,000.0 |  | $ 10,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  | 0 | $ 0 | 0 |  | $ 0 |  |  |  |  |  |  |
Other NSM | Term Loan | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  | 1,400,000 |  | 1,400,000 |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Kudu |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 300,000,000.0 |  | 300,000,000.0 |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  |  |  |  |  |  |  |  | 86,300,000 |  |  |  |
Outstanding balance |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 89,200,000 |  |  |  |
Kudu Bank Facility | Term Loan | Kudu |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount borrowed |  |  |  |  |  |  | $ 198,000,000.0 |  | $ 198,000,000.0 |  |  |  |  |  |  |  |  |
Percentage of borrowing base |  |  |  |  |  |  | 35.00% |  | 35.00% |  |  | 35.00% |  |  |  |  |  |
Remaining borrowing capacity under revolving credit facility |  |  |  |  |  |  | $ 70,700,000 |  | $ 70,700,000 |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest Reserve |  |  |  |  |  |  | 4,000,000.0 |  | $ 4,000,000.0 |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu | USD-LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  |  | 4.30% | 4.30% |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu | Base Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  |  | 0.25% | 0.25% |  |  |  |  |  |  |  |
Kudu Bank Facility | Revolving credit loan | Kudu |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 102,000,000.0 |  | $ 102,000,000.0 |  |  |  |  |  |  |  |  |
Loss on debt extinguishment |  |  |  |  |  |  |  |  | (4,100,000) |  |  |  |  |  |  |  |  |
Draw down of debt and revolving line of credit |  |  |  |  |  |  |  |  | 3,000,000.0 |  |  |  |  |  |  |  |  |
Repayments on credit facility |  |  |  |  |  |  |  |  | 92,200,000 |  |  |  |  |  |  |  |  |
First Credit Facility | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 16,300,000 |  | 16,300,000 |  |  |  |  |  |  |  |  |
First Credit Facility | Term Loan | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 11,300,000 |  | 11,300,000 |  |  |  |  |  |  |  |  |
Repayments of lines of credit |  |  |  |  |  |  | 200,000 |  | 800,000 |  |  |  |  |  |  |  |  |
Outstanding balance |  |  |  |  |  |  | 8,300,000 |  | 8,300,000 |  |  |  |  |  |  |  |  |
First Credit Facility | Revolving credit loan | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 2,000,000.0 |  | 2,000,000.0 |  |  |  |  |  |  |  |  |
Draw down of debt and revolving line of credit |  |  |  |  |  |  |  |  | 300,000 |  |  |  |  |  |  |  |  |
Repayments of lines of credit |  |  |  |  |  |  | 300,000 |  |  |  |  |  |  |  |  |  |  |
First Credit Facility | Delayed Draw Term Loans | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 3,000,000.0 |  | 3,000,000.0 |  |  |  |  |  |  |  |  |
Second Credit Facility | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 15,000,000.0 |  | 15,000,000.0 |  |  |  |  |  |  |  |  |
Second Credit Facility | Term Loan | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 9,000,000.0 |  | 9,000,000.0 |  |  |  |  |  |  |  |  |
Repayments of lines of credit |  |  |  |  |  |  | 200,000 |  | 400,000 |  |  |  |  |  |  |  |  |
Outstanding balance |  |  |  |  |  |  | 8,500,000 |  | 8,500,000 |  |  |  |  |  |  |  |  |
Second Credit Facility | Revolving credit loan | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 2,000,000.0 |  | 2,000,000.0 |  |  |  |  |  |  |  |  |
Second Credit Facility | Delayed Draw Term Loans | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 4,000,000.0 |  | 4,000,000.0 |  |  |  |  |  |  |  |  |
Third Credit Facility | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  | 4,000,000.0 |  | 4,000,000.0 |  |  |  |  |  |  |  |  |
Third Credit Facility | Term Loan | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of lines of credit |  |  |  |  |  |  | 500,000 |  | 500,000 |  |  |  |  |  |  |  |  |
Outstanding balance |  |  |  |  |  |  | $ 3,000,000.0 |  | $ 3,000,000.0 |  |  |  |  |  |  |  |  |

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- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
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