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Contract Balances (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2019
USD ($)
Allowance for Doubtful Accounts Receivable [Roll Forward]  
Balance at Beginning of Period $ 16,956
Charged to Cost and Expenses 18,496
Deductions (16,485)
Balance at End of Period 18,967
Balance at Beginning of Period 624,626
Recognition of unearned revenue (1,596,576)
Deferral of revenue 1,589,358
Balance at End of Period $ 617,408
Remaining performance obligations true