Debt Facility - Additional Information (Detail)		1 Months Ended	6 Months Ended
	Apr. 28, 2017 USD ($) Tranche $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) Tranche shares
Line Of Credit Facility [Line Items]
Prepayment fee percentage	6.00%
Warrants issued to purchase shares of common stock | shares			1,644,035
Amortization of debt discount			$ 400,000
April 2017 Warrants [Member]
Line Of Credit Facility [Line Items]
Warrants, expected term			10 years
April 2017 Warrants [Member] | Volatility [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			71.42
April 2017 Warrants [Member] | Risk Free Interest Rate [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			2.33
April 2017 Warrants [Member] | Dividend Yield [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			0
April 2017 Warrants [Member] | Common Stock [Member]
Line Of Credit Facility [Line Items]
Warrants issued to purchase shares of common stock | shares	24,725
Exercise price of warrants per share | $ / shares	$ 9.10
Warrants expiration term	10 years
Warrants expiration date	Apr. 28, 2027
June 2017 Warrants [Member]
Line Of Credit Facility [Line Items]
Warrants, expected term			10 years
June 2017 Warrants [Member] | Volatility [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			71.57
June 2017 Warrants [Member] | Risk Free Interest Rate [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			2.16
June 2017 Warrants [Member] | Dividend Yield [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			0
June 2017 Warrants [Member] | Common Stock [Member]
Line Of Credit Facility [Line Items]
Warrants issued to purchase shares of common stock | shares	41,736
Exercise price of warrants per share | $ / shares	$ 5.39
Warrants expiration term	10 years
Warrants expiration date	Jun. 15, 2027
December 2018 Warrants [Member]
Line Of Credit Facility [Line Items]
Warrants, expected term			10 years
Amortization of debt discount			$ 100,000
December 2018 Warrants [Member] | Volatility [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			80.09
December 2018 Warrants [Member] | Risk Free Interest Rate [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			2.98
December 2018 Warrants [Member] | Dividend Yield [Member]
Line Of Credit Facility [Line Items]
Warrants, expected rate			0
December 2018 Warrants [Member] | Common Stock [Member]
Line Of Credit Facility [Line Items]
Warrants issued to purchase shares of common stock | shares		11,332
Exercise price of warrants per share | $ / shares		$ 8.824
Warrants expiration term		10 years
Warrants expiration date		Dec. 04, 2028
Loan and Security Agreement [Member] | Silicon Valley Bank [Member]
Line Of Credit Facility [Line Items]
Number of tranches | Tranche	2		2
Loan and security agreement, maximum amount	$ 15,000,000	$ 45,000,000
Loan agreement amendment date	Oct. 31, 2017
Loan and Security Agreement [Member] | Silicon Valley Bank [Member] | Term Loan
Line Of Credit Facility [Line Items]
Interest rate, basis spread		3.00%
Debt instrument interest only payment maturity date		2020-10
Debt instrument principal and interest payment period		25 months
Debt instrument extended interest only payment maturity date		2022-11
Prepayment fee percentage		6.00%
Payments of debt issuance costs		$ 100,000
Prepayment description			(i) a prepayment fee (3.0% of funded amounts in months 1-12, 2.0% of funded amounts in months 13-24, and 1.0% thereafter); and (ii) an end of term charge equal to 6.0% of the amount of principal borrowed.
Loan and Security Agreement [Member] | Silicon Valley Bank [Member] | Term Loan | Prepayment Fee 1-12 Months [Member]
Line Of Credit Facility [Line Items]
Prepayment fee percentage		3.00%
Loan and Security Agreement [Member] | Silicon Valley Bank [Member] | Term Loan | Prepayment Fee 13-24 Months [Member]
Line Of Credit Facility [Line Items]
Prepayment fee percentage		2.00%
Loan and Security Agreement [Member] | Silicon Valley Bank [Member] | Term Loan | Prepayment Fee Thereafter [Member]
Line Of Credit Facility [Line Items]
Prepayment fee percentage		1.00%
Loan and Security Agreement [Member] | Silicon Valley Bank [Member] | First Tranche [Member]
Line Of Credit Facility [Line Items]
Loan and security agreement, maximum amount		$ 25,000,000
Line of credit refinance outstanding amount		15,000,000
Loan and Security Agreement [Member] | Silicon Valley Bank [Member] | Second Tranche [Member]
Line Of Credit Facility [Line Items]
Loan and security agreement, amount available upon certain condition		$ 20,000,000
Line of credit facility available upon request prior to period		Sep. 30, 2019
Cash collateral amount		$ 20,000,000
Market capitalization requirements and thresholds		$ 200,000,000