Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($)		12 Months Ended
	Sep. 09, 2020	Dec. 31, 2021	Dec. 31, 2020	Mar. 11, 2021	Nov. 13, 2020	Dec. 11, 2018
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporation month and year		2013-12
State of incorporation		DE
Net loss		$ 89,800,000	$ 78,300,000
Accumulated deficit		$ 367,463,000	$ 277,707,000
Spero Therapeutics LLC [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Merger date		Jun. 30, 2017
At-The-Market Offering Program [Member] | Cantor Fitzgerald & Co [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock available for issuance		$ 344,205
At-The-Market Offering Program [Member] | Sales Agreement [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock available for issuance					$ 34,000,000.0
At-The-Market Offering Program [Member] | Sales Agreement [Member] | Cantor Fitzgerald & Co [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Gross proceeds from issuance of common stock	$ 15,400,000
Common stock value remaining available for issuance	$ 34,600,000				$ 34,000,000.0
At-The-Market Offering Program [Member] | Sales Agreement [Member] | Cantor Fitzgerald & Co [Member] | Maximum [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Authorized offering value				$ 300,000,000.0		$ 200,000,000.0
Common stock available for issuance				$ 75,000,000.0		$ 50,000,000.0