Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Direct Amount									$ 3,108,687	$ 2,993,157	$ 2,808,764
Assumed From Other Companies									25,010	24,399	25,831
Ceded to Other Companies									451,883	420,385	398,366
Net premiums earned	$ 704,899	$ 694,541	$ 630,671	$ 651,703	$ 668,359	$ 653,620	$ 642,619	$ 632,573	$ 2,681,814	$ 2,597,171	$ 2,436,229
Percentage of Amount Assumed to Net									1.00%	1.00%	1.00%
Accident and Health Insurance Segment [Member]
Direct Amount									$ 13	$ 17	$ 19
Assumed From Other Companies									0	0	0
Ceded to Other Companies									13	17	19
Net premiums earned									$ 0	$ 0	$ 0
Percentage of Amount Assumed to Net									0.00%	0.00%	0.00%
Property and liability insurance [Member]
Direct Amount									$ 3,108,674	$ 2,993,140	$ 2,808,745
Assumed From Other Companies									25,010	24,399	25,831
Ceded to Other Companies									451,870	420,368	398,347
Net premiums earned									$ 2,681,814	$ 2,597,171	$ 2,436,229
Percentage of Amount Assumed to Net									1.00%	1.00%	1.00%