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Description of Business and Significant Accounting Policies - Concentrations of Credit Risk and Significant Clients (Details) - financial_institution | 12 Months Ended |
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Dec. 31, 2017 | Dec. 31, 2016
Accounting Policies [Abstract] |  |
Number of financial institutions holding cash and cash equivalents and marketable securities | 1 | 1
Percentage of revenue from major customer | 17.60% |

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- Definition Concentration Risk, Number of Financial Institutions Holding Cash and Cash Equivalents and Marketable Securities + References No definition available. + Details
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- Definition Percentage of Revenue from a Major Customer. + References No definition available. + Details
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- References No definition available. + Details
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