Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details)

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Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Marketable Security Positions Held By The Company As Of December 31, 2020    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable security gains (losses), net $ (600)  
Marketable Security Positions Held By The Company As Of December 31, 2019    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable security gains (losses), net   $ 2,200
Fair Value, Measurements, Recurring | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash, cash equivalents, restricted cash and restricted cash equivalents 66,822 78,444
Marketable securities 7,597 7,936
Fair Value, Measurements, Recurring | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash, cash equivalents, restricted cash and restricted cash equivalents 0 0
Marketable securities 0 0
Fair Value, Measurements, Recurring | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash, cash equivalents, restricted cash and restricted cash equivalents 0 0
Marketable securities $ 0 $ 0