Investment Securities - Investments Held on Deposit or as Collateral (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021
Investment securities
Percentage of investments recorded at fair value	72.00%	68.00%
Investments held in trusts	$ 500.5	$ 479.5
Assets held by insurance regulators	4.6	4.8
Outrigger Re \| Cash and Short Term Investments
Investment securities
Investment owned, balance	203.7
HG Global Senior Notes \| Secured Debt
Investment securities
Interest reserve account	31.2
Letter of Credit \| Short-term investments \| Asset Pledged as Collateral
Investment securities
Investments pledged as collateral	90.3	50.0
Lloyds Bank
Investment securities
Investments held in trusts	137.4	113.8
Fair value investments	$ 319.2	$ 342.8

Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 825
-Section 50
-Paragraph 1A
-URI https://asc.fasb.org/extlink&oid=123600598&loc=SL75763979-209797

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The amount of cash, securities, or other assets held by a third-party trustee pursuant to the terms of an agreement which assets are available to be used by beneficiaries to that agreement only within the specific terms thereof and which agreement is expected to terminate within one year of the balance sheet date (or operating cycle, if longer) at which time the assets held-in-trust will be released or forfeited.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(b))
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The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 2
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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Investments Held In Trusts

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