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Debt - Narrative (Details) |  | 3 Months Ended | 9 Months Ended |  |  |  |  |  |  |  |  |
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Apr. 07, 2020 GBP (£) | Apr. 07, 2020 USD ($) | Sep. 30, 2020 USD ($) credit_facility | Sep. 30, 2019 USD ($) | Sep. 30, 2020 GBP (£) | Sep. 30, 2020 USD ($) credit_facility | Sep. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) | Jun. 04, 2020 GBP (£) | Jun. 04, 2020 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 23, 2019 USD ($) | Jun. 30, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jun. 15, 2018 USD ($) | May 11, 2018 USD ($)
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  | $ 291,400,000 |  |  |  |  |  |  |  |  | $ 234,000,000.0 |  |  |  |  |  |
Number of Secured Credit Facilities | credit_facility |  |  | 2 |  |  | 2 |  |  |  |  |  |  |  |  |  |  |
Debt |  |  | $ 359,400,000 |  |  | $ 359,400,000 |  |  |  |  |  | $ 283,500,000 |  |  |  |  |
Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  | $ 270,200,000 |  |  | $ 270,200,000 |  |  |  |  |  | $ 219,200,000 |  |  |  |  |
Specialty Insurance Distribution (NSM) | Interest Rate Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, fixed interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.97% |
Derivative, variable interest rate |  |  | 1.00% |  |  | 1.00% |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount borrowed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000.0
NSM Bank Facility | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount borrowed |  |  | $ 275,000,000.0 |  |  | $ 275,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Percentage of discounted future cash flows |  |  |  |  | 10.00% | 10.00% |  |  |  |  |  |  |  |  |  |  |
Debt, weighted average interest rate, all-in |  |  | 6.91% |  |  | 6.91% |  |  |  |  |  | 6.60% |  |  |  |  |
Debt |  |  | $ 275,000,000.0 | $ 221,900,000 |  | $ 275,000,000.0 | $ 221,900,000 | $ 273,400,000 |  |  |  | $ 221,300,000 |  | $ 222,300,000 | $ 180,400,000 |  |
NSM Bank Facility | Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  | $ 268,800,000 |  |  | $ 268,800,000 |  |  |  |  |  | $ 217,400,000 |  |  |  |  |
Effective percentage |  |  | 7.40% |  |  | 7.40% |  |  |  |  |  | 7.50% |  |  |  |  |
Long-term Debt, Gross |  |  | $ 275,000,000.0 |  |  | $ 275,000,000.0 |  |  |  |  |  | $ 221,300,000 |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount borrowed |  | 276,400,000 |  |  |  |  |  |  | £ 42,500,000 | $ 52,400,000 | 224,000,000.0 |  |  |  |  |  |
Proceeds from borrowings | £ 42,500,000 | $ 52,400,000 | 0 | 0 | £ 42,500,000 | 52,400,000 | 42,900,000 |  |  |  |  |  |  |  |  |  |
Foreign currency translation |  |  | $ 2,300,000 | 0 |  | $ 2,600,000 | 0 |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | Designated as Hedging Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt, weighted average interest rate, all-in |  |  | 6.84% |  |  | 6.84% |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | Interest Rate Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 151,000,000.0 |
Debt, weighted average interest rate, all-in |  |  |  |  |  |  |  | 6.98% |  |  |  |  |  |  |  |  |
Hedged liability, fair value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 151,000,000.0 |
Derivative, fixed interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.97% |
Debt |  |  | $ 148,000,000.0 |  |  | $ 148,000,000.0 |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | Interest Rate Swap | Designated as Hedging Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt, weighted average interest rate, all-in |  |  | 8.72% |  |  | 8.72% |  |  |  |  |  |  |  |  |  |  |
Debt |  |  | $ 148,000,000.0 |  |  | $ 148,000,000.0 |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | Interest Rate Swap | Not Designated as Hedging Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  | $ 127,000,000.0 |  |  | $ 127,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Effective percentage |  |  | 7.03% |  |  | 7.03% |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | USD-LIBOR | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 4.25% | 4.25% | 5.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | USD-LIBOR | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, interest rate, increase (decrease) |  |  |  |  | 1.25% | 1.25% |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 4.75% | 4.75% | 6.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | GBP-LIBOR | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 6.00% | 6.00% |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Term Loan | Specialty Insurance Distribution (NSM) | GBP-LIBOR | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, interest rate, increase (decrease) |  |  |  |  | 1.25% | 1.25% |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 6.50% | 6.50% |  |  |  |  |  |  |  |  |  |  |
Derivative, cap interest rate |  |  | 1.25% |  |  | 1.25% |  |  |  |  |  |  |  |  |  |  |
NSM Bank Facility | Revolving credit loan | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  | $ 15,000,000.0 |  |  |  |  |  |  |  |  | $ 10,000,000.0 |  |  |  |  |  |
Proceeds from borrowings |  |  | $ 0 | $ 0 |  | $ 0 | $ 6,500,000 |  |  |  |  |  |  |  |  |  |
Other NSM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  |  |  |  |  |  | $ 1,800,000 |  |  |  |  |
Other NSM | Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective percentage |  |  | 2.80% |  |  | 2.80% |  |  |  |  |  | 3.00% |  |  |  |  |
Other NSM | Term Loan | Specialty Insurance Distribution (NSM) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  | $ 1,600,000 |  |  | $ 1,600,000 |  |  |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Kudu |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  | $ 124,000,000.0 |  |  |  |
Kudu Bank Facility | Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  |  |  |  |  |  | $ 53,600,000 |  |  |  |  |
Effective percentage |  |  | 8.40% |  |  | 8.40% |  |  |  |  |  | 8.30% |  |  |  |  |
Long-term Debt, Gross |  |  | $ 74,000,000.0 |  |  | $ 74,000,000.0 |  |  |  |  |  | $ 57,000,000.0 |  |  |  |  |
Kudu Bank Facility | Term Loan | Kudu |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  | 57,000,000.0 |  |  |  |
Debt |  |  | 74,000,000.0 |  |  | 74,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of long-term debt |  |  |  |  |  | $ 17,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu | USD-LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 1.00% | 1.00% |  |  |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu | USD-LIBOR | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 5.50% | 5.50% |  |  |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu | USD-LIBOR | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 6.25% | 6.25% |  |  |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu | Prime Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 1.00% | 1.00% |  |  |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu | Prime Rate | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 4.50% | 4.50% |  |  |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Line of Credit | Kudu | Prime Rate | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 5.25% | 5.25% |  |  |  |  |  |  |  |  |  |  |
Kudu Bank Facility | Delayed Draw Term Loans | Kudu |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  | 62,000,000.0 |  |  |  |
Kudu Bank Facility | Revolving credit loan | Kudu |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  | $ 5,000,000.0 |  |  |  |
First Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  | 16,300,000 |  |  | $ 16,300,000 |  |  |  |  |  |  |  |  |  |  |
First Credit Facility | Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  | 11,300,000 |  |  | 11,300,000 |  |  |  |  |  |  |  |  |  |  |
Long-term Debt, Gross |  |  | 9,800,000 |  |  | 9,800,000 |  |  |  |  |  |  |  |  |  |  |
First Credit Facility | Delayed Draw Term Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  | 3,000,000.0 |  |  | 3,000,000.0 |  |  |  |  |  |  |  |  |  |  |
First Credit Facility | Revolving credit loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  | 2,000,000.0 |  |  | 2,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Second Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  | 15,000,000.0 |  |  | 15,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Second Credit Facility | Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  | 9,000,000.0 |  |  | 9,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Long-term Debt, Gross |  |  | 9,000,000.0 |  |  | 9,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Second Credit Facility | Delayed Draw Term Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  | 4,000,000.0 |  |  | 4,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Second Credit Facility | Revolving credit loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  | $ 2,000,000.0 |  |  | $ 2,000,000.0 |  |  |  |  |  |  |  |  |  |  |

X
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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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- Definition Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6036836-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Incremental percentage increase (decrease) in the stated rate on a debt instrument. + References No definition available. + Details
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- Definition Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract. + References No definition available. + Details
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- Definition Variable interest rate in effect as of the balance sheet date related to the interest rate derivative. + References No definition available. + Details
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- Definition Amount of liability hedged in fair value hedging relationship. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4EE -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL109999712-113959 + Details
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- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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