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Leases - Schedule of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 40.3	$ 37.6
Lease liability	$ 41.0	$ 38.3
Operating lease, weighted average incremental borrowing rate, percent	4.80%	4.60%
HG/BAM
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 9.6	$ 10.1
Lease liability	9.6	10.1
Ark
Lessee, Lease, Description [Line Items]
ROU lease asset	4.9
Lease liability	4.9
Specialty Insurance Distribution (NSM)
Lessee, Lease, Description [Line Items]
ROU lease asset	16.0	17.1
Lease liability	16.0	17.1
Asset Management (Kudu)
Lessee, Lease, Description [Line Items]
ROU lease asset	2.0	2.0
Lease liability	2.0	2.0
Other Operations
Lessee, Lease, Description [Line Items]
ROU lease asset	7.8	8.4
Lease liability	$ 8.5	$ 9.1

X

- 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

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Balance Type:	credit
Period Type:	instant

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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

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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

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