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Marketable Securities - Unrealized losses (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Unrealized losses    
Equity securities, net unrealized losses $ (2,336)  
Corporate Securities    
Fair value    
Fair value, less than 12 months 141,723 $ 46,303
Fair value, 12 months or greater 38,232 13,992
Unrealized losses    
Unrealized losses, Less than 12 months (401) (24)
Unrealized losses, 12 months or greater $ (189) $ (6)