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Leases - Schedule of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions | Sep. 30, 2020 | Dec. 31, 2019 | Jan. 01, 2019
--- | --- | --- | ---
Lessee, Lease, Description [Line Items] |  |  |
ROU lease asset | $ 38.3 | $ 22.6 | $ 23.2
Lease liability | $ 39.1 | $ 22.8 | $ 23.2
Operating lease, weighted average incremental borrowing rate, percent | 4.60% | 4.60% |
HG/BAM |  |  |
Lessee, Lease, Description [Line Items] |  |  |
ROU lease asset | $ 9.9 | $ 10.4 |
Lease liability | 9.9 | 10.4 |
Specialty Insurance Distribution (NSM) |  |  |
Lessee, Lease, Description [Line Items] |  |  |
ROU lease asset | 17.0 | 4.8 |
Lease liability | 17.0 | 4.8 |
Asset Management (Kudu) |  |  |
Lessee, Lease, Description [Line Items] |  |  |
ROU lease asset | 2.1 | 2.3 |
Lease liability | 2.1 | 2.3 |
Other Operations |  |  |
Lessee, Lease, Description [Line Items] |  |  |
ROU lease asset | 9.3 | 5.1 |
Lease liability | $ 10.1 | $ 5.3 |

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Present value of lessee's discounted obligation for lease payments from operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977 + Details
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- Definition Amount of lessee's right to use underlying asset under operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977 + Details
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- Definition Weighted average discount rate for operating lease calculated at point in time. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(4) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971 + Details
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