Schedule IV. Reinsurance (Details) - Property and casualty business - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount	$ 1,106,327	$ 1,133,583	$ 1,083,981
Ceded to Other Companies	84,924	72,023	63,487
Assumed From Other Companies	33,679	25,412	16,957
Net Amount	$ 1,055,082	$ 1,086,972	$ 1,037,451
Percentage of Amount Assumed to Net Earned	3.19%	2.34%	1.63%