SCHEDULE IV - REINSURANCE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Premiums earned
Gross Amount	$ 15.8	$ 28.7	$ 28.6
Assumed	15.9	2.5	4.7
Net earned premiums	1,691.6	1,440.9	1,076.7
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Premiums earned
Gross Amount	1,004.2	848.1	655.5
Ceded	(504.6)	(364.0)	(280.8)
Assumed	1,088.2	925.6	668.7
Net earned premiums	$ 1,587.8	$ 1,409.7	$ 1,043.4
Percentage of Amount Assumed to Net	68.50%	65.70%	64.10%
Financial Guarantee (HG Global)
Premiums earned
Gross Amount	$ 15.8	$ 28.7	$ 28.6
Ceded	0.0	0.0	0.0
Assumed	15.9	2.5	4.7
Net earned premiums	$ 31.7	$ 31.2	$ 33.3
Percentage of Amount Assumed to Net	50.20%	8.00%	14.10%
Bamboo Captive
Premiums earned
Gross Amount	$ 0.0
Ceded	(4.0)
Assumed	43.4
Net earned premiums	$ 39.4
Percentage of Amount Assumed to Net	110.20%
Bamboo CRV
Premiums earned
Gross Amount	$ 0.0
Ceded	0.0
Assumed	32.7
Net earned premiums	$ 32.7
Percentage of Amount Assumed to Net	100.00%