Historical Loss and LAE Development - Reserve Development (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
(Favorable)/Unfavorable Reserve Development
(Favorable)/unfavorable reserve development	$ (125,463)	$ (101,053)	$ (75,284)
Casualty Segment
(Favorable)/Unfavorable Reserve Development
(Favorable)/unfavorable reserve development	(108,632)	(75,075)	(62,497)
Property segment
(Favorable)/Unfavorable Reserve Development
(Favorable)/unfavorable reserve development	(10,981)	(13,019)	(4,461)
Surety Segment
(Favorable)/Unfavorable Reserve Development
(Favorable)/unfavorable reserve development	$ (5,850)	$ (12,959)	$ (8,326)