Investments - Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($) security	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Investment Holdings [Line Items]
Accrued investment income	$ 25,328		$ 21,259
Number of debt securities for which there is an allowance for credit losses | security	19
Losses on fixed income securities	$ 2,000
Number of debt securities in an unrealized loss position for which an allowance for credit losses has not been recorded | security	1,547
Unrealized loss	$ 329,563		280,222
Unrealized losses as percentage of fixed income portfolio cost basis	11.00%
Unrealized losses relative to total invested assets (as a percent)	10.00%
Number of unrealized loss positions | security	1,547
Number of securities in unrealized loss positions for 12 months or longer | security	1,200
Maximum
Investment Holdings [Line Items]
Losses on fixed income securities		$ 1,000
Fixed Income Securities
Investment Holdings [Line Items]
Accrued investment income	$ 23,000		$ 20,000