Notes Payable - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
Mar. 31, 2019	Mar. 31, 2019	Mar. 31, 2018
Debt Instrument [Line Items]
Interest expense		$ 478,000
Loan Agreement [Member]
Debt Instrument [Line Items]
Interest expense		500,000	$ 0
Term Loan [Member] \| Loan Agreement [Member] \| Hercules Capital, Inc [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loan	$ 15,000,000	15,000,000
Debt discount discount and issuance costs	400,000	400,000
Payments of fee	$ 300,000	300,000
Debt instrument, percentage of final payment due at maturity to outstanding debt	5.55%
Final fee payment due at maturity to outstanding debt	$ 800,000	$ 800,000
Percentage of effective interest rate	12.70%	12.70%

Debt instrument, percentage of final payment due at maturity to outstanding.

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Amount of the fee that accompanies borrowing money under the debt instrument.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

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- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

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Amount of interest payable on debt, including, but not limited to, trade payables.

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