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Notes Payable - Additional Information (Detail) - USD ($) |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Dec. 29, 2017 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Debt Instrument [Line Items] |  |  |  |  |  |
Proceeds from issuance of notes payable | $ 20,000,000 |  |  |  |  |
Unrestricted cash, cash equivalents and marketable securities |  | $ 82,000,000 |  | $ 82,000,000 |  |
Credit facility default amount |  | 300,000 |  | 300,000 |  |
Maximum [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Aggregate value of cash maintained by Australian subsidiary, limit |  |  |  | 4,000,000 |  |
Term Loan [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Maximum borrowings under term loan | $ 20,000,000 | $ 16,400,000 |  | $ 16,400,000 |  |
Debt facility description |  |  |  | Upon entering into the Term Loan, the Company became obligated to make monthly, interest-only payments until March 29, 2019 and, thereafter, to pay 33 consecutive, equal monthly installments of principal and interest from April 1, 2019 through December 1, 2021. The outstanding Term Loan bears a variable interest at an annual rate of 1.25% above the prime rate, which at September 30, 2019 was 5.0%. In addition, a final payment equal to 8.0% of the Term Loan is due upon the earlier of the maturity date, acceleration of the Term Loan or prepayment of all or part of the Term Loan. |  |
Debt maturity date | Dec. 01, 2021 |  |  |  |  |
Debt facility interest rate description |  |  |  | 1.25% above the prime rate |  |
Debt facility variable interest at annual rate | 1.25% |  |  |  |  |
Debt facility effective interest rate |  | 5.00% |  | 5.00% |  |
Debt facility fee percentage | 8.00% |  |  |  |  |
Charges to interest expense of debt outstanding | $ 1,600,000 |  |  |  |  |
Loan agreement minimum liquidity required |  | $ 17,200,000 |  | $ 17,200,000 |  | $ 21,000,000
Debt facility covenant description |  |  |  | Further, from 45 days after the Term Loan was entered in, the Company has met its obligation to maintain a balance of unrestricted cash, cash equivalents and marketable securities at Silicon Valley Bank in an amount not less than the greater of (i) $55.0 million and (ii) sixty-five percent (65%) of all the Company’s cash, cash equivalents and marketable securities. If the Company does not meet this requirement it will not be considered an event of default provided it immediately secures 87.5% of the principal balance in a restricted cash account. |  |
Percentage of principal balance to be secured in restricted cash account for not to be considered an event of default |  |  |  | 87.50% |  |
Interest expense on term loan |  | 400,000 | $ 500,000 | $ 1,400,000 | $ 1,400,000 |
Debt facility effective interest rate |  |  |  | 9.40% |  |
Term Loan [Member] | Minimum [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Percentage equivalent of cash, cash equivalents and marketable securities balance |  |  |  | 105.00% |  |
Unrestricted cash, cash equivalents and marketable securities |  | $ 55,000,000 |  | $ 55,000,000 |  |
Percentage of cash, cash equivalents and marketable securities |  | 65.00% |  | 65.00% |  |

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