Government Contracts - Additional Information (Detail) $ in Thousands		1 Months Ended			12 Months Ended
	Jul. 01, 2019 USD ($)	May 31, 2021 USD ($) Option	Jul. 31, 2018 USD ($)	Jun. 30, 2016 USD ($) Option	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) Option	Sep. 30, 2022 USD ($)	Jan. 19, 2022 USD ($)	Jan. 31, 2020 USD ($)	May 31, 2019 USD ($)
Government Contracts [Line Items]
Grant revenue					$ 53,509	$ 18,256
BARDA and DTRA [Member]
Government Contracts [Line Items]
Maximum potential funding from government contract					9,700
BARDA and Speros Achievement of Specified Milestones [Member]
Government Contracts [Line Items]
Potential grant amount exercised					12,700
Grant [Member] | Minimum [Member] | DoD, CDMRP and JWMRP [Member]
Government Contracts [Line Items]
Grant revenue						4,500
SPR206 [Member] | DoD, CDMRP and JWMRP [Member]
Government Contracts [Line Items]
Award received for clinical development	$ 5,900
Non-dilutive funding period	4 years
BARDA [Member]
Government Contracts [Line Items]
Potential contract amount awarded			$ 44,200					$ 59,700
Potential amount additional funding awarded								12,900
Overall potential award increased								$ 46,900
Award received for clinical development							$ 12,900
BARDA [Member] | Base Period Contracts [Member]
Government Contracts [Line Items]
Potential amount initial funding awarded			$ 15,700							$ 18,200
Potential amount additional funding awarded										2,500
Overall potential award increased										$ 46,800
Contract term			3 years
BARDA [Member] | Grant [Member]
Government Contracts [Line Items]
Grant revenue					2,200	9,900
BARDA [Member] | First Option [Member]
Government Contracts [Line Items]
Potential amount additional funding awarded									$ 15,900
Potential amount increase in committed funding									34,000
BARDA [Member] | Second Option [member]
Government Contracts [Line Items]
Potential grant amount awarded									$ 12,700
DTRA [Member] | Maximum [Member]
Government Contracts [Line Items]
Potential amount additional funding awarded					10,000
U.S. Department of Defense [Member] | Grant [Member] | Minimum [Member]
Government Contracts [Line Items]
Grant revenue					1,000
Niaid [Member]
Government Contracts [Line Items]
Potential amount additional funding awarded					100
Niaid [Member] | Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member]
Government Contracts [Line Items]
Maximum potential funding from government contract				$ 6,500
Number of option period for funding from government contract | Option				3
Niaid [Member] | Grant [Member] | Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member]
Government Contracts [Line Items]
Grant revenue						400
Niaid [Member] | SPR206 [Member]
Government Contracts [Line Items]
Contract term		5 years
Potential amount increase in committed funding					6,200
Maximum potential funding from government contract					23,500
Grant revenue					1,700	$ 400
Award received for clinical development		$ 23,400
Number of option period for funding from government contract | Option		5
Niaid [Member] | SPR206 [Member] | Maximum [Member]
Government Contracts [Line Items]
Potential amount increase in committed funding					2,200
Niaid [Member] | SPR206 [Member] | Minimum [Member]
Government Contracts [Line Items]
Potential amount increase in committed funding					2,100
Niaid [Member] | First Option [Member] | Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member]
Government Contracts [Line Items]
Number of option period for funding from government contract | Option						2
Committed amount from government contract						$ 5,900
Niaid [Member] | First Option [Member] | SPR206 [Member]
Government Contracts [Line Items]
Committed amount from government contract					$ 4,000