Term Loan - Additional Information (Detail)		12 Months Ended
Aug. 21, 2018 USD ($) Tranches	Dec. 31, 2018 USD ($) $ / shares shares
Debt Instrument [Line Items]
Amount borrowed		$ 5,000,000
Silicon Valley Bank [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Number of common stock issuable \| shares		220,588
Silicon Valley Bank [Member] \| Term Loans [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loans	$ 15,000,000
Number of tranches \| Tranches	3
Loan agreement, description		Contemporaneously with executing the Loan Agreement, the Company drew down the first $5.0 million tranche. The second and third $5.0 million tranches may be drawn only upon the achievement of certain development milestones.
Loan agreement, frequency of payments		Monthly
Interest payment description		Borrowings under the Loan Agreement bear interest at the greater of (i) 6.0% or (ii) a floating per annum rate 1.0% above the prime rate (for an interest rate of 6.50% at December 31, 2018), with interest only due and payable monthly, until March 1, 2020 (unless extended under the conditions set forth in the Loan Agreement), at which time interest and principal will be due and payable in equal monthly payments; and are subject to a final payment fee equal to 6.75% of the aggregate principal amount.
Final payment fee as percent of aggregate principal amount of borrowing	6.75%
Minimium requirement of cash and cash equivalents held with bank		$ 10,000,000
Minimium percentage requirement of cash and cash equivalents held with bank		80.00%
Applicable interest rate of loan		5.00%
Loan payment fee		$ 300,000
Interest expense		$ 200,000
Silicon Valley Bank [Member] \| Term Loans [Member] \| Prepayment Prior To August 21,2019 [Member]
Debt Instrument [Line Items]
Principal prepayment fee percentage		3.00%
Silicon Valley Bank [Member] \| Term Loans [Member] \| Prepayment After August 21,2019 But Prior To August 21,2020 [Member]
Debt Instrument [Line Items]
Principal prepayment fee percentage		2.00%
Silicon Valley Bank [Member] \| Term Loans [Member] \| Prepayment on August 21,2020 Or Prior To Maturity Date on August 1, 2022 [Member]
Debt Instrument [Line Items]
Principal prepayment fee percentage		1.00%
Silicon Valley Bank [Member] \| Term Loans [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Loan agreement bear interest rate		6.50%
Variable rate on borrowings above prime rate, percentage	1.00%
Silicon Valley Bank [Member] \| Term Loans [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Loan agreement bear interest rate	6.00%
Silicon Valley Bank [Member] \| Term Loans [Member] \| Tranche One [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loans	$ 5,000,000
Amount borrowed	5,000,000
Effective interest rate of loan		9.89%
Unamortized debt discount		$ 100,000
Amortization of debt discount and accrual of final payment		$ 100,000
Silicon Valley Bank [Member] \| Term Loans [Member] \| Tranche Two [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loans	5,000,000
Silicon Valley Bank [Member] \| Term Loans [Member] \| Tranche Three [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loans	$ 5,000,000
Silicon Valley Bank [Member] \| Warrants to Purchase Common Stock [Member]
Debt Instrument [Line Items]
Warrant expiration date		Aug. 21, 2028
Silicon Valley Bank [Member] \| Warrants to Purchase Common Stock [Member] \| Term Loans [Member]
Debt Instrument [Line Items]
Warrants issued in connection with loan \| shares		73,529
Price per share of issued warrants \| $ / shares		$ 1.87

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