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Cash Equivalents and Investments - Schedule of Fair Value of Securities, not Including Cash (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | $ 54,117 | $ 73,427
Gross Unrealized Gains | 3 | 3
Gross Unrealized Losses |  | (19)
Estimated Fair Value | 54,120 | 73,411
Cash equivalents | 23,613 | 15,091
Short-term investments | 30,507 | 58,320
Total cash equivalents and investments | 54,120 | 73,411
Money Market Funds |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | 23,613 | 10,606
Estimated Fair Value | 23,613 | 10,606
U.S. Government Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | 3,476 | 9,976
Gross Unrealized Gains | 1 |
Gross Unrealized Losses |  | (1)
Estimated Fair Value | 3,477 | 9,975
Corporate Notes |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | 11,284 | 16,514
Gross Unrealized Gains | 2 | 3
Gross Unrealized Losses |  | (18)
Estimated Fair Value | 11,286 | 16,499
Commercial Paper |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | 15,744 | 36,331
Estimated Fair Value | $ 15,744 | $ 36,331

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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- Definition Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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- Definition Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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