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Schedule II - Valuation and Qualifying Accounts (Details) - Reserve for Uncollectible Accounts [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Movement in Reserve [Roll Forward]    
Balance at beginning of year $ 305,000 $ 305,000
Additions - charged to cost and expenses 613,556 258,542
Additions - recoveries 54,653 51,900
Deductions 318,209 310,442
Balance at end of year $ 655,000 $ 305,000