Debt - Narrative (Details) € in Millions								1 Months Ended				3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
	Jul. 21, 2025 USD ($)	Jul. 16, 2025 USD ($)	Jul. 04, 2025 USD ($)	Jan. 24, 2025 USD ($)	Apr. 29, 2022 USD ($)	Sep. 08, 2021 USD ($)	Aug. 11, 2021 USD ($)	Sep. 30, 2025 USD ($) credit_facility	Jul. 31, 2023	Sep. 30, 2021 USD ($)	Jul. 31, 2021	Sep. 30, 2025 USD ($) credit_facility	Sep. 30, 2024 USD ($)	Sep. 30, 2021 USD ($) transaction	Dec. 31, 2025 USD ($)	Sep. 30, 2025 USD ($) credit_facility	Sep. 30, 2024 USD ($)	Dec. 31, 2025 USD ($)	Sep. 30, 2025 EUR (€) credit_facility	Sep. 16, 2025 USD ($)	Sep. 02, 2025 USD ($)	Jul. 20, 2025	Jun. 30, 2025 USD ($)	Mar. 18, 2025	Mar. 12, 2025 USD ($)	Dec. 31, 2024 USD ($)	Sep. 17, 2024 USD ($)	Aug. 22, 2024 USD ($)	Jul. 31, 2024	Jun. 30, 2024 USD ($)	Jun. 28, 2024 USD ($)	Dec. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 16, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jul. 13, 2021 USD ($)	Jul. 13, 2021 EUR (€)	Mar. 23, 2021 USD ($)
Debt Instrument
Debt								$ 870,400,000				$ 870,400,000				$ 870,400,000										$ 562,500,000
Draw down of debt and revolving lines of credit																212,400,000	$ 15,500,000
Subsidiary - HG Global | Interest Rate Cap
Debt Instrument
Notional amount																												$ 150,000,000						$ 150,000,000
Maximum interest rate																												10.76%						9.76%
Kudu | Interest Rate Cap
Debt Instrument
Notional amount																											$ 150,000,000
Maximum interest rate																											8.95%
Subsidiary - Bamboo | Interest Rate Cap
Debt Instrument
Notional amount																									$ 80,000,000
Maximum interest rate																									10.00%
Subsidiary - Distinguished | Interest Rate Cap
Debt Instrument
Notional amount																				$ 70,000,000
Maximum interest rate																				10.50%
Ark 2021 Subordinated Notes
Debt Instrument
Debt								159,700,000				159,700,000				159,700,000										154,500,000
Ark 2021 Subordinated Notes | Subordinated Debt
Debt Instrument
Face value										$ 163,300,000				$ 163,300,000
Number of transactions | transaction														3
Proceeds from debt, net of debt issuance costs														$ 157,800,000
Debt								159,700,000				159,700,000				159,700,000										154,500,000
Ark 2021 Subordinated Notes Tranche 1 | Subordinated Debt
Debt Instrument
Face value																																				$ 46,300,000	€ 39.1
Amount borrowed								45,900,000				45,900,000				45,900,000			€ 39.1							41,100,000
Ark 2021 Subordinated Notes Tranche 1 | Subordinated Debt | Euro Interbank Offered Rate (EURIBOR)
Debt Instrument
Basis spread on variable rate											5.75%
Ark 2021 Subordinated Notes Tranche 2 | Subordinated Debt
Debt Instrument
Face value							$ 47,000,000
Amount borrowed								47,000,000.0				47,000,000.0				47,000,000.0										47,000,000.0
Ark 2021 Subordinated Notes Tranche 2 | Subordinated Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument
Basis spread on variable rate							5.75%
Kudu Credit Facility
Debt Instrument
Debt								274,300,000				274,300,000				274,300,000										238,600,000
Kudu Credit Facility | Secured Debt
Debt Instrument
Face value	$ 500,000,000																														$ 350,000,000							$ 300,000,000
Basis spread on variable rate	3.10%								0.26%
Amount borrowed								282,300,000				282,300,000	$ 225,300,000			282,300,000	225,300,000						$ 253,300,000			245,300,000				$ 210,300,000		$ 210,300,000
Stated margin	7.25%								4.30%																				4.45%
Interest reserve account								$ 7,900,000				$ 7,900,000				$ 7,900,000										$ 15,100,000
Debt service coverage ratio								3.5				3.5				3.5			3.5					2.5		2.5
Debt covenant, loan to value percent	40.00%																					50.00%
Total interest rate									4.56%
Debt	$ 253,300,000							$ 274,300,000				$ 274,300,000				$ 274,300,000										$ 238,600,000
Floating rate	8.75%
Fixed rate	7.65%
Debt covenant, maximum loan to value percent								22.80%				22.80%				22.80%			22.80%
Percentage of borrowing base								35.00%				35.00%				35.00%			35.00%
Draw down of debt and revolving lines of credit												$ 29,000,000.0	$ 15,000,000.0			$ 37,000,000.0	$ 15,000,000.0
Kudu Credit Facility | Secured Debt | Debt Covenant, Period 1
Debt Instrument
Debt covenant, loan to value percent								40.00%				40.00%				40.00%			40.00%
Kudu Credit Facility | Secured Debt | Debt Covenant, Period 2
Debt Instrument
Debt covenant, loan to value percent								25.00%				25.00%				25.00%			25.00%
Kudu Credit Facility | Secured Debt | Debt Covenant, Period 3
Debt Instrument
Debt covenant, loan to value percent								15.00%				15.00%				15.00%			15.00%
Kudu Credit Facility | Secured Debt | Debt Covenant, Period 4
Debt Instrument
Debt covenant, loan to value percent								0.00%				0.00%				0.00%			0.00%
Kudu Credit Facility | Secured Debt | Forecast
Debt Instrument
Debt service coverage ratio															3.0			3.0
Kudu Credit Facility | Secured Debt | Secured Overnight Financing Rate (SOFR)
Debt Instrument
Basis spread on variable rate						0.26%	0.26%
Ark 2021 Subordinated Notes Tranche 3 | Subordinated Debt
Debt Instrument
Face value						$ 70,000,000
Debt instrument, period for interest rate increase						10 years
Additional interest rate																1.00%
Solvency capital requirement										120.00%
Debt to capital requirement										40.00%
Amount borrowed								$ 70,000,000.0				$ 70,000,000.0				$ 70,000,000.0										70,000,000.0
Ark 2021 Subordinated Notes Tranche 3 | Subordinated Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument
Basis spread on variable rate						6.10%
Citibank LOC Facility | Line of Credit | Letter of Credit
Debt Instrument
Total commitment under revolving credit facility																																			$ 125,000,000
Letters of credit outstanding								78,100,000				78,100,000				78,100,000
Pledged collateral								93,300,000				93,300,000				93,300,000
Lloyds LOC Facility | Line of Credit | Letter of Credit
Debt Instrument
Total commitment under revolving credit facility																																	$ 100,000,000
Letters of credit outstanding								24,900,000				24,900,000				24,900,000
Pledged collateral								30,300,000				30,300,000				30,300,000
HG Global Senior Notes
Debt Instrument
Debt								147,700,000				147,700,000				$ 147,700,000										147,400,000
HG Global Senior Notes | Senior Notes
Debt Instrument
Face value					$ 150,000,000
Additional interest rate																1.00%
Amount borrowed								150,000,000.0				150,000,000.0				$ 150,000,000.0										150,000,000.0
Stated margin					6.00%
Anniversary of funding date					5 years
Annual payments					$ 15,000,000
Interest accrued multiplier																																		8
Interest reserve account								31,800,000				31,800,000				31,800,000										29,300,000
Debt								147,700,000				147,700,000				147,700,000										147,400,000
HG Global Senior Notes | Senior Notes | Secured Overnight Financing Rate (SOFR)
Debt Instrument
Basis spread on variable rate					0.26%
Bamboo Credit Facility
Debt Instrument
Debt								104,600,000				104,600,000				104,600,000										0
Bamboo Credit Facility | Secured Debt
Debt Instrument
Face value				$ 110,000,000
Amount borrowed								$ 109,500,000				$ 109,500,000				$ 109,500,000							$ 109,700,000			0
Stated margin								4.50%				4.50%				4.50%			4.50%
Annual payments				$ 1,100,000
Debt								$ 104,600,000				$ 104,600,000				$ 104,600,000										0
Debt instrument, term				6 years
Debt instrument, periodic payment, principal				$ 800,000
Total leverage ratio				1.5				0.5				0.5				0.5			0.5
Draw down of debt and revolving lines of credit												$ 0				$ 110,000,000.0
Bamboo Credit Facility | Secured Debt | Minimum
Debt Instrument
Stated margin				4.50%
Bamboo Credit Facility | Secured Debt | Maximum
Debt Instrument
Stated margin				5.00%
Total leverage ratio								4.5				4.5				4.5			4.5
Bamboo Credit Facility | Secured Debt | Revolving Credit Facility
Debt Instrument
Total commitment under revolving credit facility				$ 10,000,000
Distinguished Credit Facility
Debt Instrument
Debt								$ 138,100,000				$ 138,100,000				$ 138,100,000										0
Distinguished Credit Facility | Secured Debt
Debt Instrument
Face value			$ 141,000,000
Amount borrowed								$ 139,800,000				$ 139,800,000				$ 139,800,000					$ 90,200,000					0
Stated margin								5.50%				5.50%				5.50%			5.50%
Debt								$ 138,100,000				$ 138,100,000				$ 138,100,000										0
Total leverage ratio			3.75					4.1				4.1				4.1			4.1
Draw down of debt and revolving lines of credit			$ 50,000,000.0					$ 50,000,000.0
Distinguished Credit Facility | Secured Debt | Minimum
Debt Instrument
Stated margin			5.25%
Distinguished Credit Facility | Secured Debt | Maximum
Debt Instrument
Stated margin			5.50%
Total leverage ratio								5.5				5.5				5.5			5.5
Distinguished Credit Facility | Secured Debt | Forecast
Debt Instrument
Debt instrument, periodic payment, principal															$ 400,000			$ 1,400,000
Distinguished Credit Facility | Secured Debt | Revolving Credit Facility
Debt Instrument
Total commitment under revolving credit facility			$ 15,000,000
Distinguished Credit Facility | Secured Debt | Delayed Draw Term Loan
Debt Instrument
Total commitment under revolving credit facility			$ 40,000,000
Other Operations debt
Debt Instrument
Debt								$ 35,400,000				$ 35,400,000				$ 35,400,000										22,000,000.0
Other Operations debt | Secured Debt
Debt Instrument
Amount borrowed								35,900,000				35,900,000				35,900,000										22,400,000
Debt								$ 35,400,000				$ 35,400,000				$ 35,400,000										$ 22,000,000.0
Secured credit facilities | credit_facility								5				5				5			5
WTM Credit Facility | Revolving Credit Facility
Debt Instrument
Debt to capital requirement		32.50%
Total commitment under revolving credit facility		$ 250,000,000
Line of credit facility, certain other adjustment		$ 3,200,000,000
WTM Credit Facility | Revolving Credit Facility | Minimum
Debt Instrument
Stated margin		1.10%
WTM Credit Facility | Revolving Credit Facility | Maximum
Debt Instrument
Stated margin		1.50%