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Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Premiums written:
Direct	$ 746,431	$ 766,394
Assumed	6,043	6,555
Ceded	(105,147)	(100,002)
Net	647,327	672,947
Premiums earned:
Direct	754,892	728,037
Assumed	6,173	6,562
Ceded	(109,362)	(102,026)
Net	651,703	632,573
Loss and loss expenses incurred:
Direct	425,795	424,657
Assumed	4,898	5,265
Ceded	(30,369)	(43,343)
Net	400,324	$ 386,579
COVID-19 [Member]
Effects of Reinsurance [Line Items]
Premium audit accrual decrease	$ 75,000

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