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Valuation and Qualifying Accounts | 12 Months Ended
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Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract] |
Valuation and Qualifying Accounts | 4. Valuation and Qualifying Accounts
|  | Balance at Beginning of Year |  |  | Charged to Expense |  |  | Deductions (1) |  |  | Balance at End of Year |
Allowance for doubtful accounts receivable: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Year ended December 31, 2017 |  | $ | 5,918 |  |  |  | 18,478 |  |  |  | (18,489 | ) |  | $ | 5,907 |
Year ended December 31, 2016 |  | $ | 5,137 |  |  |  | 18,639 |  |  |  | (17,858 | ) |  | $ | 5,918 |
Year ended December 31, 2015 |  | $ | 6,472 |  |  |  | 16,620 |  |  |  | (17,955 | ) |  | $ | 5,137 |
(1) | Deductions represent accounts written off, net of recoveries.

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- Definition The entire disclosure for any allowance and reserve accounts (their beginning and ending balances, as well as a reconciliation by type of activity during the period). Alternatively, disclosure of the required information may be within the footnotes to the financial statements or a supplemental schedule to the financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -URI http://asc.fasb.org/topic&trid=2122369 + Details
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- References No definition available. + Details
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