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Schedule of Valuation and Qualifying Accounts | 12 Months Ended
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Dec. 31, 2017
Valuation And Qualifying Accounts [Abstract] |
Schedule Of Valuation And Qualifying Accounts Disclosure [Text Block] |
| Schedule II - Valuation Accounts
|  |  |  |  |  |  | Additions |  |  |  |
|  |  |  |  | Balance at |  |  |  |  |  |  |  | Balance at
|  |  |  |  | Beginning |  | Charges to |  |  |  |  |  | End of
(in thousands) |  | of Period |  | Operations |  | Other |  | Deductions |  | Period
| Year ended December 31, 2017: |  |  |  |  |  |  |  |  |  |
|  | Allowance for doubtful accounts(1) |  | $ 2,838 |  | 1,697 |  | — |  | 4,430 |  | 105
| Year ended December 31, 2016: |  |  |  |  |  |  |  |  |  |
|  | Allowance for doubtful accounts(1) |  | $ 3,417 |  | — |  | — |  | 579 |  | 2,838
| Year ended December 31, 2015: |  |  |  |  |  |  |  |  |  |
|  | Allowance for doubtful accounts(1) |  | $ 2,943 |  | 499 |  | — |  | 25 |  | 3,417
(1) | Deductions in the allowance for doubtful accounts represent write-offs, net of recoveries, of amounts
|  | determined to be uncollectible.
See accompanying Report of Independent Registered Public Accounting Firm incorporated herein by reference.

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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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