Investment Information - Net investment Income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net investment income:
Gross investment income		$ 477,123	$ 608,823	$ 716,643
Investment expenses		(88,005)	(89,215)	(88,905)
Net investment income		389,118	519,608	627,738
Fixed maturities
Net investment income:
Gross investment income		330,061	412,481	505,399
Term loan investments
Net investment income:
Gross investment income		34,843	84,149	98,949
Equity securities
Net investment income:
Gross investment income		42,396	28,958	15,857
Short-term investments
Net investment income:
Gross investment income		6,928	10,840	15,820
Other
Net investment income:
Gross investment income	[1]	$ 62,895	$ 72,395	$ 80,618

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