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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2017
Accounting Policies [Abstract] |
Summary of Subsidiaries Not Wholly Owned | As of December 31, 2016, the Company consolidated the following subsidiaries that were not wholly owned:
Subsidiary |  | Relationship |  |  | Country Domiciled |  |  | Year of Inclusion |
Spero Potentiator, Inc. |  |  | Controlling interest |  |  |  | United States |  |  |  | 2014 |
Spero Europe, Ltd. |  |  | Controlling interest |  |  |  | United Kingdom |  |  |  | 2015 |
Spero Gyrase, Inc. |  |  | Controlling interest |  |  |  | United States |  |  |  | 2016 |
Spero Cantab, Inc. |  |  | Controlling interest |  |  |  | United States |  |  |  | 2016 |
Estimated Useful Lives of Assets | Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows:
|  | Estimated Useful Life
Laboratory equipment |  | 5 years
Computer software and equipment |  | 3 years
Office furniture and equipment |  | 7 years
Leasehold improvements |  | Shorter of life of lease or 5 years

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