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Summary of Significant Accounting Policies - Allowance for Doubtful Accounts and Credit Memo Reserves (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Valuation Allowance [Line Items]      
The general period to charge-off uncollectible balances of receivable, as circumstances warrant, is no later than this period of time past due 1 year    
SEC Schedule, 12-09, Allowance, Credit Loss      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of the Year $ 46,648 $ 44,290 $ 31,447
Credit Memos Charged to Revenue 36,329 38,966 37,616
Allowance for Bad Debts Charged to Expense 18,625 14,826 8,705
Other (1,568) 1,905 16,528
Deductions (56,450) (53,339) (50,006)
Balance at End of the Year $ 43,584 $ 46,648 $ 44,290