Fair Value Measurements - Fair Value Hierarchy for Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financial Assets:
Fixed maturities	$ 627.4	$ 650.3
Short term investments	45.8	99.8
Total	673.2	750.1
Financial Liabilities:
Fair value of Public and Private warrant liabilities (less than)	0.1
Corporate debt securities
Financial Assets:
Fixed maturities	449.9	530.2
U.S. Government obligations
Financial Assets:
Fixed maturities	175.9	117.3
Asset-backed securities
Financial Assets:
Fixed maturities	1.6	2.8
Warrant liability
Financial Liabilities:
Warrant liability	0.0	0.3
Level 1
Financial Assets:
Fixed maturities	0.0	0.0
Short term investments	0.0	0.0
Total	0.0	0.0
Level 1 | Corporate debt securities
Financial Assets:
Fixed maturities	0.0	0.0
Level 1 | U.S. Government obligations
Financial Assets:
Fixed maturities	0.0	0.0
Level 1 | Asset-backed securities
Financial Assets:
Fixed maturities	0.0	0.0
Level 1 | Warrant liability
Financial Liabilities:
Warrant liability	0.0	0.0
Level 2
Financial Assets:
Fixed maturities	627.4	650.3
Short term investments	45.8	99.8
Total	673.2	750.1
Level 2 | Corporate debt securities
Financial Assets:
Fixed maturities	449.9	530.2
Level 2 | U.S. Government obligations
Financial Assets:
Fixed maturities	175.9	117.3
Level 2 | Asset-backed securities
Financial Assets:
Fixed maturities	1.6	2.8
Level 2 | Warrant liability
Financial Liabilities:
Warrant liability	0.0	0.0
Level 3
Financial Assets:
Fixed maturities	0.0	0.0
Short term investments	0.0	0.0
Total	0.0	0.0
Level 3 | Corporate debt securities
Financial Assets:
Fixed maturities	0.0	0.0
Level 3 | U.S. Government obligations
Financial Assets:
Fixed maturities	0.0	0.0
Level 3 | Asset-backed securities
Financial Assets:
Fixed maturities	0.0	0.0
Level 3 | Warrant liability
Financial Liabilities:
Warrant liability	$ 0.0	$ 0.3