Annual report pursuant to Section 13 and 15(d)

Short-term and Long-term Investments, Restricted Deposits - Narrative (Details)

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Short-term and Long-term Investments, Restricted Deposits - Narrative (Details)
12 Months Ended
Dec. 31, 2019
position
Schedule Of Investments And Restricted Deposits By Type [Line Items]  
Positions from which gross unrealized losses were generated 682
Total number of positions 4,529
Commercial mortgage- backed securities  
Schedule Of Investments And Restricted Deposits By Type [Line Items]  
Investments that carry rating of A A plus, weighted average, duration 4 years
External Credit Rating, Investment Grade | Rated Securities  
Schedule Of Investments And Restricted Deposits By Type [Line Items]  
Percentage of investment grade investments rated by nationally recognized statistical rating organizations 97.00%