Term Loan - Additional Information (Detail)		3 Months Ended		6 Months Ended
	Aug. 21, 2018 USD ($) Tranches	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)
Debt Instrument [Line Items]
Amount borrowed		$ 5,000,000		$ 5,000,000
Silicon Valley Bank [Member] | Maximum [Member]
Debt Instrument [Line Items]
Number of common stock issuable | shares		147,059		147,059
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 $5.0 million tranche expired on June 30, 2019 and the third $5.0 million tranche may be drawn only upon the achievement of a certain development milestone.
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 June 30, 2019), with interest only due and payable monthly, until March 1, 2020, at which time interest and principal will be due and payable monthly in equal monthly payments; 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%
Minimum requirement of cash and cash equivalents held with bank		$ 10,000,000		$ 10,000,000
Minimum 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		$ 100,000	$ 0	$ 200,000	$ 0
Silicon Valley Bank [Member] | Term Loans [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Loan agreement bear interest rate		6.50%		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%		9.89%
Unamortized debt discount		$ 100,000		$ 100,000
Silicon Valley Bank [Member] | Term Loans [Member] | Tranche Two [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loans	5,000,000
Expiration date				Jun. 30, 2019
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		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		$ 1.87