License, Collaboration, and Funding Agreements - Additional Information (Detail)				1 Months Ended			3 Months Ended		9 Months Ended
	Apr. 12, 2019 $ / shares shares	Mar. 13, 2019	Dec. 12, 2018 USD ($)	Dec. 31, 2016 USD ($)	Aug. 31, 2015 USD ($) shares	Aug. 31, 2014 USD ($) $ / shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Collaboration License And Funding Arrangements [Line Items]
Issuance of preferred stock (in shares) | shares	5,670,000
Reverse stock split, conversion ratio		0.1667			0.1667
Shares issued price per share (in usd per share) | $ / shares	$ 11.00
Other income							$ 52,000	$ 0	$ 201,000	$ 0
Proceeds from transfer of non-financial assets							900,000		$ 896,000
AUSTRIA
Collaboration License And Funding Arrangements [Line Items]
Grant income (in percentage)									14.00%
Genzyme Agreement
Collaboration License And Funding Arrangements [Line Items]
Upfront payments						$ 50,000
Cash payment					$ 300,000
Issuance of preferred stock (in shares) | shares					107,371
Research and development expense					$ 734,000
Shares issued price per share (in usd per share) | $ / shares						$ 0.01
Future milestone payments									$ 25,000,000.0
Payment on obligation under license agreement									0
Georgetown Agreement
Collaboration License And Funding Arrangements [Line Items]
Payment on obligation under license agreement									0
One time upfront payment				$ 50,000
Milestone payments				800,000
Milestone payment obligation							0		0
BIDMC Agreement
Collaboration License And Funding Arrangements [Line Items]
Payment on obligation under license agreement									0
One time upfront payment				$ 20,000
Research and Development Incentive
Collaboration License And Funding Arrangements [Line Items]
Grant receivable							1,700,000		1,700,000
Other income							$ 226,000		$ 226,000
Janssen License and Option Agreement | Janssen Pharmaceuticals Incorporation
Collaboration License And Funding Arrangements [Line Items]
Payables from related parties			$ 3,500,000
Payment received from related parties			3,500,000
Janssen License and Option Agreement | Janssen Pharmaceuticals Incorporation | Patents
Collaboration License And Funding Arrangements [Line Items]
Proceeds from transfer of non-financial assets			$ 500,000