Investments - Principal geographic distribution of municipal bonds (Details)	Dec. 31, 2022	Dec. 31, 2021
Texas
Municipal Bonds
Percentage of municipal bonds carrying value	9.60%	8.70%
California
Municipal Bonds
Percentage of municipal bonds carrying value	8.50%	11.80%
New York
Municipal Bonds
Percentage of municipal bonds carrying value	6.70%	5.10%
Illinois
Municipal Bonds
Percentage of municipal bonds carrying value	5.60%	4.10%
Pennsylvania
Municipal Bonds
Percentage of municipal bonds carrying value	5.40%	5.40%
Florida
Municipal Bonds
Percentage of municipal bonds carrying value	5.00%	4.20%