Summary of Significant Accounting Policies - Additional Information (Detail)					1 Months Ended	12 Months Ended
	Nov. 27, 2019 USD ($) $ / shares	Aug. 19, 2019 USD ($)	May 08, 2019 $ / shares shares	Apr. 11, 2019 $ / shares shares	May 08, 2019 USD ($) $ / shares	Dec. 31, 2019 USD ($) segment $ / shares shares	Dec. 31, 2018 USD ($) shares
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit						$ 298,821,000	$ 261,232,000
Cash and cash equivalents						$ 6,316,000	9,140,000
Consideration from sale of stock					$ 18,300,000
Number of reportable segments | segment						1
Long-lived assets						$ 51,484,000	38,275,000
Restricted cash						455,000	455,000
Research and development						25,385,000	25,508,000
Customer Concentration Risk | Total Portfolio Investment
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk						1,000,000
Research and Development
Summary Of Significant Accounting Policies [Line Items]
Research and development						11,500,000	13,900,000
Intracutaneous Delivery System
Summary Of Significant Accounting Policies [Line Items]
Research and development						13,900,000	11,600,000
Deposit Building Lease
Summary Of Significant Accounting Policies [Line Items]
Restricted cash						300,000	300,000
Deposit Utility Provider
Summary Of Significant Accounting Policies [Line Items]
Restricted cash						100,000	100,000
Corporate Purchasing Cards
Summary Of Significant Accounting Policies [Line Items]
Restricted cash						$ 35,000	$ 35,000
Minimum | Software, Computer and Office Equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets						P2Y
Minimum | Furniture, Fixtures, Manufacturing and Laboratory Equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets						P7Y
Maximum | Customer Concentration Risk | Total Portfolio Investment
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage						10.00%
Maximum | Software, Computer and Office Equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets						P5Y
Maximum | Furniture, Fixtures, Manufacturing and Laboratory Equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets						P9Y
At-The-Market Offering
Summary Of Significant Accounting Policies [Line Items]
Price of stock sold (in USD per share) | $ / shares						$ 1.57
Consideration from sale of stock						$ 5,200,000
Offering expense, accrued						$ 100,000
Maximum aggregate offering price (up to)		$ 15,000,000.0
Commissions on proceeds from the sale of shares		3.00%
Shares issued in transaction (in shares) | shares						3,599,141
Commissions and other offering expenses						$ 200,000
Public Stock Offering
Summary Of Significant Accounting Policies [Line Items]
Price of stock sold (in USD per share) | $ / shares				$ 3.29
Shares issued in transaction (in shares) | shares				5,000,000
Over-Allotment
Summary Of Significant Accounting Policies [Line Items]
Price of stock sold (in USD per share) | $ / shares			$ 3.29		$ 3.29
Shares issued in transaction (in shares) | shares			750,000
Common Stock
Summary Of Significant Accounting Policies [Line Items]
Common stock shares issued (in shares) | shares							10,000,000
Price of stock sold (in USD per share) | $ / shares	$ 1.45
Consideration from sale of stock	$ 3,100,000
Offering expense, accrued						$ 100,000
Common Stock | At-The-Market Offering
Summary Of Significant Accounting Policies [Line Items]
Common stock shares issued (in shares) | shares						3,599,141
Common Stock | Public Stock Offering
Summary Of Significant Accounting Policies [Line Items]
Common stock shares issued (in shares) | shares						5,750,000