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Accounting Policies Accounts Receivable (Details) | 12 Months Ended
--- | ---
Dec. 31, 2017 USD ($) customer | Dec. 31, 2016 USD ($)
Concentration Risk [Line Items] |  |
Allowance for doubtful accounts | $ | $ 0 | $ 0
Accounts Receivable | Customer Concentration Risk |  |
Concentration Risk [Line Items] |  |
Number of customers | customer | 1 |
Concentration risk, percentage | 22.00% | 36.60%

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- Definition For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.4) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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