Schedule VI. Supplementary Insurance Information Concerning Property-Casualty Insurance Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Line Items]
Current year	$ 2,123,876	$ 1,390,767	$ 1,902,424
Prior years	(26,855)	(270,749)	(40,996)
Consolidated Subsidiaries
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs	663,991	476,661	426,551
Reserves for Unpaid Claims and Claim Adjustment Expenses	9,384,349	6,076,271	5,080,408
Discount, if any, Deducted	0	0	0
Unearned Premiums	2,530,975	1,716,021	1,477,609
Earned Premiums	3,338,403	1,976,129	1,717,575
Net Investment Income	423,833	261,866	222,209
Current year	2,123,876	1,390,767	1,902,424
Prior years		(270,749)	(40,996)
Amortization of Deferred Policy Acquisition Costs	762,232	432,989	346,892
Paid Claims and Claim Adjustment Expenses	1,098,054	894,769	974,825
Net Premiums Written	$ 3,381,493	$ 2,131,902	$ 1,871,325