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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair Value Measurements - Financial Instruments Based on Observable Inputs (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Oct. 20, 2020	Jul. 02, 2020
Senior Notes \| Senior Notes Due 2030
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Interest rate, stated percentage	4.875%	4.875%		4.875%
Junior Subordinated Debt \| Fixed Rate Reset Junior Subordinated notes due 2041
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Interest rate, stated percentage	6.625%	6.625%	6.625%
Fair Value \| Preference securities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	$ 56.9	$ 55.6
Fair Value \| Level 2 \| Senior Notes \| 4.875% Senior notes due 2030
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	326.3	273.1
Fair Value \| Level 2 \| Senior Subordinated Notes \| 6.625% Fixed Rate Reset Junior Subordinated notes due 2041
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	123.8	121.6
Carrying Value \| Preference securities
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	58.4	58.4
Carrying Value \| Level 2 \| Senior Notes \| 4.875% Senior notes due 2030
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	325.6	325.0
Carrying Value \| Level 2 \| Senior Subordinated Notes \| 6.625% Fixed Rate Reset Junior Subordinated notes due 2041
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	$ 123.2	$ 123.2