Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Schedule of Changes in Estimated Fair Value of Derivative Asset) (Details)

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Fair Value Measurements (Schedule of Changes in Estimated Fair Value of Derivative Asset) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Balance as of January 1, 2021      
Acquisition of Whinstone     37,761  
Change in fair value of derivative asset $ 17,536 17,536
Balance as of June 30, 2021 30,360   30,360  
Significant unobservable inputs (Level 3) [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Balance as of January 1, 2021      
Acquisition of Whinstone     13,967  
Change in fair value of derivative asset     16,393  
Balance as of June 30, 2021 $ 30,360   $ 30,360