Organization, Nature of the Business, COVID-19 Risk and Basis of Presentation - Additional Information (Detail)				1 Months Ended		3 Months Ended						9 Months Ended
	Nov. 10, 2021 USD ($)	Aug. 14, 2020 USD ($)	May 28, 2020 $ / shares shares	Jul. 31, 2021 USD ($) shares	Jun. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / shares shares
Common stock, par value per share | $ / shares						$ 0.001						$ 0.001		$ 0.001
Common stock, shares issued | shares						17,710,450						17,710,450		15,367,730
Proceeds from issuance of common stock												$ 19,885,000	$ 75,350,000
Net loss						$ 16,805,000	$ 12,609,000	$ 12,088,000	$ 10,274,000	$ 11,330,000	$ 6,674,000	41,502,000	$ 28,278,000
Accumulated deficit						(107,116,000)						(107,116,000)		$ (65,614,000)
Cash, cash equivalents and marketable securities						$ 78,000,000.0						$ 78,000,000.0
Common Stock [Member]
Issuance of common stock | shares | shares						2,342,720
Private Offering [Member]
Proceeds from issuance common stock and warrants net offering costs					$ 75,400,000
ATM Offering [Member] | Common Stock [Member]
Issuance of common stock | shares | shares				2,342,720
Proceeds from issuance of common stock				$ 20,500,000
ATM Offering [Member] | Common Stock [Member] | Subsequent Event [Member]
Gross sales proceeds under sales agreement remaining amount	$ 29,200,000
ATM Offering [Member] | Common Stock [Member] | Maximum [Member]
Aggregate sale of shares of our common stock		$ 50,000,000
Zafgen [Member]
Reverse stock split of common stock			1-for-12
Common stock, par value per share | $ / shares			$ 0.001
Cash, cash equivalents, restricted cash and marketable debt securities acquired merger					$ 42,900,000
Zafgen [Member] | Merger Agreement [Member]
Exchange rate of shares issued per share			60,912.5005
Common stock, shares issued | shares			6,091,250
Chondrial [Member] | Merger Agreement [Member]
Common stock, par value per share | $ / shares			$ 0.001