Fair Value (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of public equity portfolio	$ 1,400,000		$ 1,300,000
Other invested assets	789,014		757,167
Asset Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Market Value	3,997,891		3,581,729
Internally Managed Portfolio, Collateralized Loan Obligations [Member] | Asset Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Market Value	2,100,000		2,000,000
Market Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Transfer in and/or (out) of Level 3
Fair Value [Member] | Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other invested assets	299,600		286,600
Fixed Maturities [Member] | Market Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Market Value	$ 2,100,000		$ 2,100,000