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Loan and Security Agreement - Additional Information (Details) | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |  |
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Feb. 29, 2020 USD ($) Installment $ / shares shares | Aug. 31, 2017 USD ($) Installment | Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Dec. 31, 2019 USD ($) | Oct. 01, 2018 shares | Jul. 31, 2018 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Interest payable |  |  | $ 200,000 |  | $ 200,000 |  | $ 400,000 |  |
Debt, non-current |  |  | 24,281,000 |  | 24,281,000 |  | 8,876,000 |  |
Loan and accretion of debt discount |  |  | 100,000 | $ 85,000 | 200,000 | $ 175,000 |  |  |
Interest expense, debt |  |  | $ 600,000 | $ 300,000 | $ 1,000,000.0 | $ 600,000 |  |  |
Average interest rate |  |  | 8.07% | 8.87% | 8.08% | 8.88% |  |  |
Two Thousand Seventeen Warrants |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Estimated fair value portion of preferred stock |  |  |  |  |  |  |  |  | $ 300,000
Series E Redeemable Convertible Preferred Stock |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Warrant to purchase stock | shares |  |  |  |  |  |  |  | 46,359 |
August 2017 Loan | Floating Rate |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Interest charges on loan |  | 7.39% |  |  |  |  |  |  |
August 2017 Loan | LIBOR |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Interest charges on loan |  | 6.40% |  |  |  |  |  |  |
Description of interest charges on loan |  |  |  |  | the sum of the 30-day U.S. Dollar London Interbank Offered Rate (“LIBOR”) plus 6.40%. |  |  |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Warrant to purchase stock | shares | 81,257 |  |  |  |  |  |  |  |
Exercise price per share | $ / shares | $ 9.23 |  |  |  |  |  |  |  |
Estimated fair value upon issuance of warrants | $ 600,000 |  |  |  |  |  |  |  |
Debt, non-current |  |  | $ 25,000,000.0 |  | $ 25,000,000.0 |  |  |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | August 2017 Loan |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Borrowed amount |  | $ 15,000,000.0 |  |  |  |  |  |  |
Debt outstanding amount |  |  |  |  |  |  | $ 10,000,000.0 |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | August 2017 Loan | March 2019 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Number of monthly installments | Installment |  | 30 |  |  |  |  |  |  |
Payment terms, description |  |  |  |  | The loan was due in 30 monthly installments from March 2019 |  |  |  |
Repayment installment, start date, month and year |  | 2019-03 |  |  |  |  |  |  |
Repayment installment, end date, month and year |  | 2021-08 |  |  |  |  |  |  |
Frequency of interest-only payments |  |  |  |  | monthly payments |  |  |  |
Interest-only payments, maturity month and year |  | 2019-03 |  |  |  |  |  |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | Term A Loan |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Borrowed amount | 25,000,000.0 |  |  |  |  |  |  |  |
Term loan maximum borrowing capacity | 25,000,000.0 |  |  |  |  |  |  |  |
Repayment of outstanding principal amount | $ 9,600,000 |  |  |  |  |  |  |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | Term Loans |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Number of monthly installments | Installment | 24 |  |  |  |  |  |  |  |
Payment terms, description |  |  |  |  | The Term Loans mature on March 1, 2024 (the “Maturity Date”) and will be interest-only through March 1, 2022, followed by 24 equal monthly payments of principal and interest. |  |  |  |
Interest charges on loan | 8.07% |  |  |  |  |  |  |  |
Description of interest charges on loan |  |  |  |  | The Term Loans will bear interest at a floating per annum rate equal to the greater of (i) 8.07% or (ii) the sum of (a) the greater of (1) the thirty (30) day U.S. LIBOR rate reported in the Wall Street Journal on the last business day of the month that immediately precedes the month in which the interest will accrue or (2) 1.67%, plus (b) 6.40%. |  |  |  |
Debt instrument, maturity date | Mar. 01, 2024 |  |  |  |  |  |  |  |
Debt instrument interest only payments maturity date | Mar. 01, 2022 |  |  |  |  |  |  |  |
Floor percent of thirty days libor | 1.67% |  |  |  |  |  |  |  |
Final payment fee percentage | 3.83% |  |  |  |  |  |  |  |
Interest payable | $ 1,000,000.0 |  |  |  |  |  |  |  |
Principal amount Prepayment amount percentage to be paid before first anniversary | 3.00% |  |  |  |  |  |  |  |
Principal amount Prepayment amount percentage to be paid between first and second anniversary | 2.00% |  |  |  |  |  |  |  |
Principal amount Prepayment amount percentage to be paid to be paid thereafter and prior to maturity | 1.00% |  |  |  |  |  |  |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | Term Loans | Maximum |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Additional borrowing amount | $ 5,000,000.0 |  |  |  |  |  |  |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | Term Loans | LIBOR |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Interest charges on loan | 6.40% |  |  |  |  |  |  |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | Term B Loan | Minimum |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Upfront payment received | $ 50,000,000.0 |  |  |  |  |  |  |  |

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