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Cash and Marketable Securities (Narrative) (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Cash and Marketable Securities [Abstract] |  |  |  |  |
Marketable Securities, Realized Gain (Loss) | $ 0 | $ 0 | $ 0 | $ 0 |
Impairment charges due to declines in the vale of debt securities | $ 0 | $ 0 | 0 | $ 0 |
Unrealized losses on marketable securities |  |  | $ 0 |  | $ 0

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- Definition Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI). + References No definition available. + Details
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- Definition Amount of unrealized gain (loss) on investment in marketable security. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(c)) -URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227 + Details
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- Definition Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI http://asc.fasb.org/extlink&oid=118954083&loc=SL6284422-111562 + Details
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