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Debt - Summary of Debt Outstanding (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument
Total debt	$ 429.7	$ 376.4
Weighted average interest rate	7.10%	7.00%
Ark | Ark Subordinated Debt
Debt Instrument
Amount borrowed	$ 44.1	$ 0.0
Effective percentage	4.60%
NSM Bank Facility
Debt Instrument
Effective percentage	8.50%	8.40%
NSM Bank Facility | Book Value
Debt Instrument
Total debt	$ 271.5	$ 271.3
Other NSM debt
Debt Instrument
Total debt		1.3
Other NSM debt | Book Value
Debt Instrument
Total debt	1.2	1.3
Kudu Credit Facility | Book Value
Debt Instrument
Total debt	95.9	0.0
Kudu Bank Facility | Book Value
Debt Instrument
Total debt	0.0	86.3
Ark Alesco Note | Ark Subordinated Debt
Debt Instrument
Amount borrowed	30.0
Ark Dekania Note | Ark Subordinated Debt
Debt Instrument
Amount borrowed	14.1
Term Loan | NSM Bank Facility
Debt Instrument
Amount borrowed	277.3	277.4
Unamortized issuance cost	(5.8)	(6.1)
Total debt	$ 271.5	$ 271.3
Effective percentage	7.60%	7.50%
Term Loan | Other NSM debt
Debt Instrument
Effective percentage	2.30%	2.50%
Term Loan | Kudu Credit Facility
Debt Instrument
Amount borrowed	$ 102.0
Unamortized issuance cost	$ (6.1)
Effective percentage	5.20%
Term Loan | Kudu Bank Facility
Debt Instrument
Amount borrowed		$ 89.2
Unamortized issuance cost		(2.9)
Total debt		$ 86.3
Effective percentage		8.30%
Term Loan | Other Operations
Debt Instrument
Amount borrowed	$ 17.5	$ 18.0
Unamortized issuance cost	$ (0.5)	(0.5)
Total debt		$ 17.5
Effective percentage	7.60%	7.40%

X

- 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

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-Publisher FASB
-Name Accounting Standards Codification
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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
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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
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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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- Definition

Debt, Weighted Average Interest Rate Excluding Amortization Of Debt Issuance Costs

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