SCHEDULE III - SUPPLEMENTARY INSURANCE INFORMATION (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
HG Global/BAM
SUPPLEMENTARY INSURANCE INFORMATION
Deferred Acquisition Costs	$ 40.1	$ 36.0	$ 33.1
Future Policy Benefits, Losses, Claims and Loss Expenses	0.0	0.0	0.0
Unearned Premiums	325.8	298.3	266.3
Other Policy Claims and Benefits Payable	0.0	0.0	0.0
Premiums Earned	31.2	33.3	26.9
Net Investment Income	31.7	21.5	17.5
Benefits, Claims, Losses and Settlement Expenses	0.0	0.0	0.0
Amortization of Deferred Acquisition Costs	8.6	11.2	8.3
Other Operating Expenses	0.4	0.4	0.4
Premiums Written	58.6	65.1	55.8
Ark/WM Outrigger
SUPPLEMENTARY INSURANCE INFORMATION
Deferred Acquisition Costs	145.3	127.2	100.8
Future Policy Benefits, Losses, Claims and Loss Expenses	1,605.1	1,296.5	894.7
Unearned Premiums	743.6	623.2	495.9
Other Policy Claims and Benefits Payable	0.0	0.0	0.0
Premiums Earned	1,409.7	1,043.4	637.3
Net Investment Income	61.4	16.3	2.9
Benefits, Claims, Losses and Settlement Expenses	726.8	536.4	314.8
Amortization of Deferred Acquisition Costs	273.1	238.3	111.3
Other Operating Expenses	113.6	78.7	64.6
Premiums Written	$ 1,520.9	$ 1,195.2	$ 859.1