Government Contracts - Additional Information (Detail) $ in Thousands		1 Months Ended			3 Months Ended		12 Months Ended
	Jul. 01, 2019 USD ($)	May 31, 2021 USD ($) Option	Jul. 31, 2018 USD ($)	Jun. 30, 2016 USD ($) Option	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($) Option	Jan. 19, 2022 USD ($)	Jan. 31, 2020 USD ($)	May 31, 2019 USD ($)
Government Contracts [Line Items]
Grant revenue					$ 2,069	$ 7,300
BARDA and DTRA [Member]
Government Contracts [Line Items]
Maximum potential funding from government contract					69,700
Potential grant amount exercised					12,700
Grant [Member] | DoD, CDMRP and JWMRP [Member] | Maximum [Member]
Government Contracts [Line Items]
Grant revenue					900
Grant [Member] | DoD, CDMRP and JWMRP [Member] | Minimum [Member]
Government Contracts [Line Items]
Grant revenue						600
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
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					700	6,300
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
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					0	$ 400
Niaid [Member] | SPR206 [Member]
Government Contracts [Line Items]
Contract term		5 years
Award received for clinical development		$ 23,400
Number of option period for funding from government contract | Option		5
Committed amount from government contract					2,100
Maximum received fund					$ 300
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