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Investments - Other (Details)
6 Months Ended 12 Months Ended
Jun. 30, 2022
USD ($)
item
Dec. 31, 2021
USD ($)
Marketable Securities [Line Items]    
Available-for-sale investments $ 1,072,241,000 $ 1,218,279,000
Short term investments 5,000 0
Alternative investments fair value $ 42,911,000 $ 38,570,000
Period of advance notice before quarter end 45 days  
Transfers from Level 1 to Level 2 $ 0  
Transfers from Level 2 to Level 1 $ 0  
Number of level 3 securities held | item 1  
Subprime mortgage debt securities    
Marketable Securities [Line Items]    
Securities held $ 0