Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Principles (Accounts Receivable and Allowance for Doubtful Receivables) (Details)

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Summary of Significant Accounting Principles (Accounts Receivable and Allowance for Doubtful Receivables) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Accounting Policies [Abstract]      
Number of days in allowance used n the calculation (greater than) 120 days    
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Balance at beginning of year $ 7,555 $ 0 $ 1,100
Charged to costs and expenses 10,139 8,741 0
Charged to other accounts 0 0 0
Write-offs net of recoveries 4,522 1,186 1,100
Balance at end of year 13,172 $ 7,555 $ 0
Trade Accounts Receivable      
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Balance at end of year 7,500    
Other Assets      
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Balance at end of year $ 5,700