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Fair Value Measurements and Financial Instruments - Narrative (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Fair Value Disclosures [Abstract] |  |  |
Unrealized gain (loss) | $ 0 | $ 0 | $ 0

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- Definition Amount of unrealized gain (loss) on investments in debt and equity securities classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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Period Type: | duration

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- References No definition available. + Details
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