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Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Grouping, Financial Statement Captions
Carrying value	$ 429.7	$ 376.4
Other NSM debt
Balance Sheet Grouping, Financial Statement Captions
Carrying value		1.3
Fair Value | Ark Subordinated Debt
Balance Sheet Grouping, Financial Statement Captions
Debt, fair value	44.1	0.0
Fair Value | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Debt, fair value	275.6	279.3
Fair Value | Other NSM debt
Balance Sheet Grouping, Financial Statement Captions
Debt, fair value	1.3	1.3
Fair Value | Kudu Credit Facility
Balance Sheet Grouping, Financial Statement Captions
Debt, fair value	102.0	0.0
Fair Value | Kudu Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Debt, fair value	0.0	89.3
Fair Value | Other Operations debt
Balance Sheet Grouping, Financial Statement Captions
Debt, fair value	18.3	18.8
Carrying Value | Ark Subordinated Debt
Balance Sheet Grouping, Financial Statement Captions
Carrying value	44.1	0.0
Carrying Value | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying value	271.5	271.3
Carrying Value | Other NSM debt
Balance Sheet Grouping, Financial Statement Captions
Carrying value	1.2	1.3
Carrying Value | Kudu Credit Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying value	95.9	0.0
Carrying Value | Kudu Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying value	0.0	86.3
Carrying Value | Other Operations debt
Balance Sheet Grouping, Financial Statement Captions
Carrying value	$ 17.0	$ 17.5

X

- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

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+ References

No definition available.

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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

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-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

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