Historical Loss and LAE Development - Environmental, Asbestos and Mass Tort Exposures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Unpaid losses and LAE at beginning of year
Gross	$ 2,315,637	$ 2,043,555	$ 1,750,049	$ 1,574,352
Net	1,575,548	1,435,469	1,306,320	$ 1,189,835
Asbestos and Environmental Exposures
Loss and LAE Payments (Cumulative):
Gross	142,377	141,768	139,804
Ceded	(69,696)	(69,576)	(69,219)
Net	72,681	72,192	70,585
Unpaid losses and LAE at beginning of year
Gross	26,871	25,747	22,485
Ceded	(5,786)	(5,718)	(4,619)
Net	$ 21,085	$ 20,029	$ 17,866