Investments - Special Deposits (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	$ 650.3	$ 691.4
Deposits with state insurance departments
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	11.8	6.8
Deposits with state insurance departments | New York
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	2.8	2.8
Deposits with state insurance departments | Delaware
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	2.8	0.0
Deposits with state insurance departments | Washington
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	1.2	1.2
Deposits with state insurance departments | Colorado
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	1.1	1.1
Deposits with state insurance departments | Virginia
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.8	0.3
Deposits with state insurance departments | New Mexico
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.6	0.3
Deposits with state insurance departments | North Carolina
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.6	0.3
Deposits with state insurance departments | New Jersey
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.6	0.0
Deposits with state insurance departments | Nevada
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.4	0.4
Deposits with state insurance departments | Arkansas
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.3	0.1
Deposits with state insurance departments | Florida
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.2	0.2
Deposits with state insurance departments | Massachusetts
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.2	0.1
Deposits with state insurance departments | Kansas
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.1	0.0
Deposits with state insurance departments | Kentucky
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	$ 0.1	$ 0.0