Investment Information - Net investment Income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net investment income:
Gross investment income		$ 567,322	$ 477,123	$ 608,823
Investment expenses		(70,775)	(88,005)	(89,215)
Net investment income		496,547	389,118	519,608
Fixed maturities
Net investment income:
Gross investment income		468,659	330,061	412,481
Term loan investments
Net investment income:
Gross investment income		2,038	34,843	84,149
Equity securities
Net investment income:
Gross investment income		22,497	42,396	28,958
Short-term investments
Net investment income:
Gross investment income		29,519	6,928	10,840
Other
Net investment income:
Gross investment income	[1]	$ 44,609	$ 62,895	$ 72,395

[1] Includes income distributions from investment funds and other items