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Segment Information (Accounts Receivable by Major Customer) (Details) - Accounts receivable
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Account X    
Segment Reporting Information [Line Items]    
Percentage of accounts receivable 39.00% 42.00%
Account Y    
Segment Reporting Information [Line Items]    
Percentage of accounts receivable 20.00% 26.00%
Account Z    
Segment Reporting Information [Line Items]    
Percentage of accounts receivable 7.00% 24.00%