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Cash Equivalents and Investments - Schedule of Available-for-Sale Securities Unrealized Loss Position (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
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Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale securities, unrealized loss position, Less than 12 months, Fair Value | $ 2,498 | $ 17,498
Available-for-sale securities, unrealized loss position, Less than 12 months, Unrealized Loss |  | (11)
Available-for-sale securities, unrealized loss position, Greater than 12 months, Fair Value |  | 2,993
Available-for-sale securities, unrealized loss position, Greater than 12 months, Unrealized Loss |  | (8)
Available-for-sale securities, unrealized loss position, Total, Fair Value | 2,498 | 20,491
Available-for-sale securities, unrealized loss position, Total, Unrealized Loss |  | (19)
U.S. Government Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale securities, unrealized loss position, Less than 12 months, Fair Value |  | 5,977
Available-for-sale securities, unrealized loss position, Less than 12 months, Unrealized Loss |  | (1)
Available-for-sale securities, unrealized loss position, Total, Fair Value |  | 5,977
Available-for-sale securities, unrealized loss position, Total, Unrealized Loss |  | (1)
Corporate Notes |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale securities, unrealized loss position, Less than 12 months, Fair Value | 2,498 | 11,521
Available-for-sale securities, unrealized loss position, Less than 12 months, Unrealized Loss |  | (10)
Available-for-sale securities, unrealized loss position, Greater than 12 months, Fair Value |  | 2,993
Available-for-sale securities, unrealized loss position, Greater than 12 months, Unrealized Loss |  | (8)
Available-for-sale securities, unrealized loss position, Total, Fair Value | $ 2,498 | 14,514
Available-for-sale securities, unrealized loss position, Total, Unrealized Loss |  | $ (18)

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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