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Summary of Significant Accounting Policies - Basis of Presentation, Credit Risk and Income Taxes (Details) $ in Thousands |  | 6 Months Ended |
--- | --- | --- | ---
Jan. 01, 2019 USD ($) | Jun. 30, 2020 USD ($) item segment | Dec. 31, 2019 USD ($)
Accumulated deficit |  | $ (240,691) | $ (217,145)
Cash, cash equivalents and marketable securities |  | $ 59,300 |
Concentrations of Credit Risk and Other Risks and Uncertainties |  |  |
Number of financial institutions used for cash and cash equivalent deposits | item |  | 2 |
Segments |  |  |
Number of operating segments | segment |  | 1 |
Recent accounting pronouncements |  |  |
Package of practical expedients adopted | true |  |
Use of hindsight adopted | false |  |
Operating lease right-of-use asset |  | $ 1,996 | 2,327
Operating lease liabilities |  | $ 2,760 | $ 3,188
ASU 2016-02 |  |  |
Recent accounting pronouncements |  |  |
Operating lease right-of-use asset | $ 2,800 |  |
Operating lease liabilities | 3,800 |  |
Deferred rent | $ 1,000 |  |

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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 Indicates (true false) whether practical expedient is elected to use hindsight in determining lease term and in assessing impairment of right-of-use asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 10 -Section 65 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 10 -Section 65 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984 + Details
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