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Government Contracts - Additional Information (Detail) | 1 Months Ended | 3 Months Ended | 12 Months Ended | 22 Months Ended |
--- | --- | --- | --- | --- | ---
Mar. 31, 2018 USD ($) | Feb. 28, 2018 USD ($) | Dec. 31, 2017 USD ($) | Apr. 30, 2017 USD ($) | Feb. 28, 2017 USD ($) | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) Option | Mar. 31, 2018 USD ($) Option | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2017 USD ($) Option | Dec. 31, 2016 USD ($) | Mar. 31, 2018 USD ($) Option | Mar. 12, 2018 USD ($)
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Grant revenue |  |  |  |  |  |  |  | $ 1,153,000 | $ 993,000 | $ 597,000 | $ 249,000 | $ 140,000 | $ 335,000 | $ 1,979,000 | $ 335,000 |  |
Revenue included in other receivables | $ 1,219,000 |  | $ 1,011,000 |  |  |  |  | 1,219,000 | 1,011,000 |  |  |  | 304,000 | 1,011,000 | 304,000 | $ 1,219,000 |
Amount payable under agreement | 982,000 |  | 3,470,000 |  |  |  |  | 982,000 | 3,470,000 |  |  |  | 1,139,000 | 3,470,000 | 1,139,000 | $ 982,000 |
U.S. Department of Defense [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contract term |  |  |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |
Potential grant amount awarded |  |  |  |  |  | $ 1,500,000 |  |  |  |  |  |  |  |  |  |  |
Grant revenue |  |  |  |  |  |  |  | 100,000 |  |  |  | $ 100,000 |  | 700,000 |  |  |
Revenue included in other receivables |  |  | 100,000 |  |  |  |  |  | 100,000 |  |  |  | $ 300,000 | 100,000 | $ 300,000 |  |
Niaid [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contract term |  | 12 months |  |  | 12 months |  |  |  |  |  |  |  |  |  |  |  |
Grant revenue |  |  |  |  |  |  |  | $ 500,000 |  |  |  |  |  | 400,000 |  |  |
Niaid [Member] | Base Period Contracts [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential grant amount awarded |  |  |  |  | $ 600,000 |  |  |  |  |  |  |  |  |  |  |  |
Niaid [Member] | Option Period Contracts [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contract term |  | 12 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential grant amount awarded |  |  |  |  | $ 400,000 |  |  |  |  |  |  |  |  |  |  |  |
Potential grant amount exercised |  | $ 400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Niaid [Member] | Other Receivables [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue invoiced but unpaid |  |  | 100,000 |  |  |  |  |  | 100,000 |  |  |  |  | 100,000 |  |  |
Niaid [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 |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |
Maximum received fund |  |  | 1,300,000 |  |  |  |  |  |  |  |  |  |  | $ 1,300,000 |  |  |
Maximum potential funding from government contract |  |  |  |  |  |  | $ 6,000,000 |  |  |  |  |  |  |  |  |  |
Niaid [Member] | Spero Cantab [Member] | Cantab Anti Infectives Ltd. [Member] | Cantab Agreements [Member] | First Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of option period for funding from government contract | Option |  |  |  |  |  |  |  | 2 |  |  |  |  |  | 2 |  | 2 |
Committed amount from government contract |  |  |  |  |  |  |  | $ 5,400,000 |  |  |  |  |  | $ 5,100,000 |  | $ 5,400,000 |
Niaid [Member] | Spero Cantab [Member] | Pro Bono Bio PLC [Member] | Cantab Agreements [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount paid upfront as part of agreement | 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount payable under agreement | $ 100,000 |  |  |  |  |  |  | 100,000 |  |  |  |  |  |  |  | $ 100,000 |
CARB-X [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contract term |  |  |  | 12 months |  |  |  |  |  |  |  |  |  |  |  |  |
Potential grant amount awarded |  |  |  | $ 1,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Grant revenue |  |  |  |  |  |  |  | $ 500,000 |  |  |  |  |  | 900,000 |  |  |
Revenue included in other receivables |  |  | $ 700,000 |  |  |  |  |  | $ 700,000 |  |  |  |  | $ 700,000 |  |  |
Potential grant amount exercised |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |
CARB-X [Member] | First Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government Contracts [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential grant amount awarded |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 400,000

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