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Summary Of Significant Accounting Policies (Narrative) (Details)
 12 Months Ended
Dec. 31, 2019
USD ($)
Item
shares
Dec. 31, 2018
USD ($)
shares
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2005
Item
Dec. 31, 2001
Item
Jan. 01, 2019
USD ($)
Sep. 30, 2017
USD ($)
Dec. 31, 2016
USD ($)
Summary Of Significant Accounting Policies [Line Items]                
Minimum percent of prepaid reinsurance premiums for any foreign reinsurers that were collateralized 10.00%              
Number of operating segments | Item 4              
Equity index put option contracts sold | Item       7 7      
Derivatives, number of indices | Item       2 2      
Derivative liability $ 5,584,000 $ 11,958,000            
Anti-dilutive options | shares 0 0 0          
U.S. tax rate 21.00% 21.00% 35.00%          
Operating lease right of use assets $ 161,435,000         $ 69,869,000    
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]           Other assets    
Operating lease liabilities $ 169,909,000         $ 77,270,000    
Operating Lease, Liability, Statement of Financial Position [Extensible List]           Other liabilities    
Accumulated Other Comprehensive Income [Member]                
Summary Of Significant Accounting Policies [Line Items]                
Change to beginning balance due to adoption of Accounting Standards Update 2016-01   $ (1,201,000)       $ (1,250,000) $ (1,250,000)
Retained Earnings [Member]                
Summary Of Significant Accounting Policies [Line Items]                
Change to beginning balance due to adoption of Accounting Standards Update 2016-01   $ 1,201,000     $ 0 $ 1,250,000 $ 1,250,000
Minimum [Member]                
Summary Of Significant Accounting Policies [Line Items]                
Options expiration date Feb. 24, 2020              
Maximum [Member]                
Summary Of Significant Accounting Policies [Line Items]                
Options expiration date Sep. 19, 2022              
Expired Derivative [Member]                
Summary Of Significant Accounting Policies [Line Items]                
Number of derivatives | Item 4              
Derivative liability $ 0