Reinsurance and Policy Benefits and Losses Claims and Loss Expenses Payable (Policy Benefits and Losses, Claims and Loss Expenses Payable for Property and Casualty Insurance) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reinsurance:
Unpaid losses and loss adjustment expense		$ 177,963
Total	$ 997,701		$ 997,647
Property and Casualty Insurance [Member]
Reinsurance:
Unpaid losses and loss adjustment expense		177,963		$ 209,127	$ 228,970	$ 233,554
Operating Segments [Member] | Property and Casualty Insurance [Member]
Reinsurance:
Unpaid losses and loss adjustment expense		177,963		209,127
Reinsurance losses payable		979		1,214
Total	$ 178,942	$ 178,942	$ 210,341	$ 210,341