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Investments In Securities (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 USD ($) security | Dec. 31, 2017 USD ($) security
Investments, Debt and Equity Securities [Abstract] |  |
Number of securities with unrealized losses | security | 51 | 32
Impairment amount for cost-method investments | $ | $ 0 | $ 0

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- Definition Loss recognized as a result of the initial and subsequent write-down of a long-lived asset's carrying amount to fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2921-110230 + Details
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