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Derivatives (Narrative) (Details)
 3 Months Ended 60 Months Ended
Mar. 31, 2020
USD ($)
Item
Dec. 31, 2005
Item
Dec. 31, 2019
USD ($)
Dec. 31, 2001
Item
Derivative [Line Items]        
Number of equity indices | Item   2    
Number of equity index put option contracts | Item   7   7
Number of equity index put option contracts expired | Item 5      
Equity index put option liability $ 20,958,000   $ 5,584,000  
Equity Index Put Option Contracts [Member]        
Derivative [Line Items]        
Equity index put option liability 0      
Equity Index Put Option Contracts [Member] | Fair Value [Member]        
Derivative [Line Items]        
Equity index put option liability $ 20,958,000   $ 5,584,000  
Standard & Poor's 500 Index [Member]        
Derivative [Line Items]        
Number of equity index put option contracts | Item 1      
Theoretical maximum payout occurs based on index value $ 0      
Discount factor 3.00%      
Present value of theoretical maximum payouts $ 144,636,000      
Settlement amount if contracts had expired $ 0      
Equity index if contracts had expired 2,584.59      
Standard & Poor's 500 Index [Member] | Maximum [Member]        
Derivative [Line Items]        
Estimates the probability of equity index put option contract will falling below the strike price on the exercise date 3.00%      
FTSE 100 Index [Member]        
Derivative [Line Items]        
Number of equity index put option contracts | Item 1      
Theoretical maximum payout occurs based on index value $ 0      
Estimates the probability of equity index put option contract will falling below the strike price on the exercise date 70.00%      
Discount factor 3.00%      
Present value of theoretical maximum payouts $ 40,003,000      
Settlement amount if contracts had expired $ 2,142,000      
Equity index if contracts had expired 5,671.96