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Fair Value Measurements (Details) - Recurring - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Assets:    
Marketable securities - available for sale $ 18,061 $ 11,125
Assets - fair value 18,061 11,125
Level 1    
Assets:    
Marketable securities - available for sale 0 0
Assets - fair value 0 0
Level 2    
Assets:    
Marketable securities - available for sale 18,061 11,125
Assets - fair value 18,061 11,125
Level 3    
Assets:    
Marketable securities - available for sale 0 0
Assets - fair value $ 0 $ 0