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SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - Allowance for Doubtful Accounts [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Valuation And Qualifying Accounts Disclosure [Line Items]    
Balance at beginning of year $ 0 $ 0
Additions [1] 0 0
Deductions [2] 0 0
Other [3] 0 0
Balance at end of year $ 0 $ 0
[1] Includes charges to costs and expenses.
[2] Deductions for uncollectible accounts receivable includes payments collected and devices recovered from customers.
[3] Miscellaneous activity.