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Debt - Narrative (Details) € in Millions			1 Months Ended				3 Months Ended			6 Months Ended
Debt - Narrative (Details) € in Millions	Apr. 29, 2022 USD ($)	Sep. 08, 2021 USD ($)	Sep. 30, 2021 USD ($)	Aug. 31, 2021	Jul. 31, 2021	Mar. 31, 2007 USD ($)	Jun. 30, 2022 USD ($) credit_facility	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) credit_facility	Jun. 30, 2021 USD ($)	Jun. 30, 2022 EUR (€) credit_facility	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Aug. 11, 2021 USD ($)	Jul. 13, 2021 USD ($)	Jul. 13, 2021 EUR (€)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Debt Instrument
Debt							$ 618,100,000			$ 618,100,000				$ 420,900,000
Debt covenant, maximum loan to value percent, period one							50.00%			50.00%		50.00%
Debt covenant, maximum loan to value percent, period two							40.00%			40.00%		40.00%
Debt covenant, maximum loan to value percent, period three							25.00%			25.00%		25.00%
Debt covenant, maximum loan to value percent, period four							15.00%			15.00%		15.00%
Debt covenant, maximum loan to value percent, period five							0.00%			0.00%		0.00%
Debt covenant, maximum loan to value percent							34.10%			34.10%		34.10%
Proceeds from debt										$ 203,000,000.0	$ 105,300,000
Other
Debt Instrument
Secured credit facilities \| credit_facility							5			5		5
Ark
Debt Instrument
Debt							$ 183,500,000			$ 183,500,000				185,900,000
Unsecured Subordinated Debt \| Group Ark Insurance Limited
Debt Instrument
Borrowings								$ 157,800,000
Unsecured Subordinated Debt \| Group Ark Insurance Limited \| Ark
Debt Instrument
Notes issued			$ 163,300,000					$ 163,300,000
HG Global Senior Notes \| Secured Debt
Debt Instrument
Borrowings	$ 150,000,000
Annual payments							15,000,000			15,000,000
Interest reserve account							22,000,000			$ 22,000,000
Additional interest rate										1.00%
Debt							146,300,000			$ 146,300,000
Outstanding balance							150,000,000.0			150,000,000.0
HG Global Senior Notes \| Secured Debt \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument
Basis spread on variable rate	6.30%
Ark 2007 Subordinated Notes, carrying value \| Ark Subordinated Debt
Debt Instrument
Outstanding balance							30,000,000.0			30,000,000.0				30,000,000.0
Ark 2007 Subordinated Notes, carrying value \| Junior Notes \| Ark
Debt Instrument
Debt							30,000,000			30,000,000
Face value						$ 30,000,000
Ark 2007 Subordinated Notes, carrying value \| Junior Notes \| USD-LIBOR \| Ark
Debt Instrument
Basis spread on variable rate						4.60%
Ark 2021 Notes Tranche 1
Debt Instrument
Outstanding balance \| €												€ 39.1
Ark 2021 Notes Tranche 1 \| Ark Subordinated Debt
Debt Instrument
Outstanding balance							41,500,000			41,500,000				44,200,000
Ark 2021 Notes Tranche 1 \| Unsecured Subordinated Debt \| Group Ark Insurance Limited
Debt Instrument
Notes issued																$ 46,300,000	€ 39.1
Ark 2021 Notes Tranche 1 \| Unsecured Subordinated Debt \| Group Ark Insurance Limited \| EURIBOR
Debt Instrument
Basis spread on variable rate					5.75%
Ark 2021 Notes Tranche 2 \| Ark Subordinated Debt
Debt Instrument
Outstanding balance							47,000,000			47,000,000				47,000,000.0
Ark 2021 Notes Tranche 2 \| Unsecured Subordinated Debt \| Group Ark Insurance Limited
Debt Instrument
Notes issued															$ 47,000,000
Ark 2021 Notes Tranche 2 \| Unsecured Subordinated Debt \| Group Ark Insurance Limited \| USD-LIBOR
Debt Instrument
Basis spread on variable rate				5.75%
Ark 2021 Notes Tranche 3 \| Ark Subordinated Debt
Debt Instrument
Outstanding balance							70,000,000			70,000,000				70,000,000.0
Ark 2021 Notes Tranche 3 \| Unsecured Subordinated Debt \| Group Ark Insurance Limited
Debt Instrument
Additional interest rate		1.00%
Notes issued		$ 70,000,000
Solvency capital requirement			120.00%
Debt to capital requirement			40.00%
Ark 2021 Notes Tranche 3 \| Unsecured Subordinated Debt \| Group Ark Insurance Limited \| USD-LIBOR
Debt Instrument
Basis spread on variable rate		6.10%
ING LOC Facility \| Secured Debt \| Ark \| Letter of Credit \| Uncollateralized
Debt Instrument
Total commitment under revolving credit facility														50,000,000
Citibank LOC Facility \| Short-term investments \| Asset Pledged as Collateral
Debt Instrument
Investments pledged as collateral							49,800,000			49,800,000				50,000,000
Citibank LOC Facility \| Secured Debt
Debt Instrument
Line of credit							36,200,000			36,200,000
Citibank LOC Facility \| Secured Debt \| Ark \| Letter of Credit \| Collateral Pledged
Debt Instrument
Total commitment under revolving credit facility														100,000,000
Kudu Bank Facility \| Kudu
Debt Instrument
Total commitment under revolving credit facility							300,000,000			300,000,000
Kudu Bank Facility \| Revolving Credit Facility \| Kudu
Debt Instrument
Loss on debt extinguishment										4,100,000
Kudu Bank Facility \| Line of Credit \| Kudu
Debt Instrument
Interest reserve							7,300,000			7,300,000
Kudu Bank Facility \| Term Loan \| Kudu
Debt Instrument
Borrowings							0		$ 0	0	3,000,000.0
Debt							$ 0		0	$ 0	0		$ 0	0				$ 0	$ 89,200,000
Percentage of borrowing base							35.00%			35.00%		35.00%
Remaining borrowing capacity under revolving credit facility							$ 27,800,000			$ 27,800,000
First Credit Facility \| Other
Debt Instrument
Total commitment under revolving credit facility							16,300,000			16,300,000
First Credit Facility \| Revolving Credit Facility \| Other
Debt Instrument
Total commitment under revolving credit facility							2,000,000			2,000,000
First Credit Facility \| Term Loan \| Other
Debt Instrument
Total commitment under revolving credit facility							11,300,000			11,300,000
First Credit Facility \| Delayed Draw Term Loans \| Other
Debt Instrument
Total commitment under revolving credit facility							3,000,000			3,000,000
Second Credit Facility \| Other
Debt Instrument
Total commitment under revolving credit facility							15,000,000			15,000,000
Second Credit Facility \| Revolving Credit Facility \| Other
Debt Instrument
Total commitment under revolving credit facility							2,000,000			2,000,000
Second Credit Facility \| Term Loan \| Other
Debt Instrument
Total commitment under revolving credit facility							9,000,000			9,000,000
Second Credit Facility \| Delayed Draw Term Loans \| Other
Debt Instrument
Total commitment under revolving credit facility							4,000,000			4,000,000
Third Credit Facility \| Other
Debt Instrument
Total commitment under revolving credit facility							8,000,000			8,000,000
Third Credit Facility \| Revolving Credit Facility \| Other
Debt Instrument
Proceeds from debt							19,000,000			21,000,000
Third Credit Facility \| Term Loan \| Other
Debt Instrument
Outstanding balance							35,700,000			35,700,000				$ 17,100,000
Repayments of lines of credit							1,100,000		$ 200,000	2,400,000	$ 400,000
Fourth Credit Facility \| Other
Debt Instrument
Total commitment under revolving credit facility							11,500,000			11,500,000
Fifth Credit Facility \| Other
Debt Instrument
Total commitment under revolving credit facility							$ 11,500,000			$ 11,500,000