Maximum amounts of investments by parent that would trigger the anti-dilution protection.

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- Definition

Maximum potential funding from government contract

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- Definition

Maximum received fund amount.

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No definition available.

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- Definition

Number of option period for funding from government contract.

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Number of option period for funding from government contract committed to date.

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- Definition

Proceeds from government contract

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No definition available.

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- Definition

Upfront payments.

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No definition available.

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- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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No definition available.

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- Definition

The cash outflow to reacquire common stock during the period.

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-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 15
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- Definition

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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Number of new stock issued during the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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Non-Controlling Interests - Spero Cantab - Additional Information (Detail)	1 Months Ended			3 Months Ended		12 Months Ended			22 Months Ended
	Dec. 31, 2017 USD ($)	Jul. 31, 2017 USD ($)	Jun. 30, 2016 USD ($) Option shares	Mar. 31, 2018 USD ($) Option	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) Option	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2018 USD ($) Option
Noncontrolling Interest [Line Items]
Research and development expense				$ 8,925,000	$ 5,999,000	$ 32,869,000	$ 26,333,000	$ 11,125,000
Non-controlling interest	$ 355,000			355,000		355,000	$ (3,808,000)		$ 355,000
Spero Cantab [Member]
Noncontrolling Interest [Line Items]
Ownership percentage							12.50%
Non-controlling interest	0			$ 0		0	$ 1,303,000		$ 0
Spero Cantab [Member] \| Cantab Agreements [Member]
Noncontrolling Interest [Line Items]
Common stock shares issued \| shares			125
Ownership percentage			12.50%
Common stock issued, aggregate fair value			$ 1,600,000
Upfront consideration			300,000
Non-controlling interest			1,600,000
Cash payment for repurchase of shares		$ 200,000
Spero Cantab [Member] \| Cantab Agreements [Member] \| Contingent Milestone Payments [Member]
Noncontrolling Interest [Line Items]
Cash payment for repurchase of shares		$ 100,000
Spero Cantab [Member] \| Cantab Anti Infectives Ltd. [Member] \| Cantab Agreements [Member]
Noncontrolling Interest [Line Items]
Research and development expense			$ 300,000
Spero Cantab [Member] \| Cantab Anti Infectives Ltd. [Member] \| Cantab Agreements [Member] \| Niaid [Member]
Noncontrolling Interest [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
Spero Cantab [Member] \| Cantab Anti Infectives Ltd. [Member] \| Cantab Agreements [Member] \| Niaid [Member] \| First Option [Member]
Noncontrolling Interest [Line Items]
Number of option period for funding from government contract committed to date \| Option				2		2			2
Committed amount from government contract to date				$ 5,400,000		$ 5,100,000			$ 5,400,000
Spero Cantab [Member] \| New Pharma License Holding Limited [Member] \| Cantab Agreements [Member]
Noncontrolling Interest [Line Items]
Research and development expense			1,600,000
Spero Cantab [Member] \| Pro Bono Bio PLC [Member] \| Cantab Agreements [Member]
Noncontrolling Interest [Line Items]
Maximum amounts of investments for anti-dilution protection			$ 8,000,000
Spero Cantab [Member] \| Pro Bono Bio PLC [Member] \| Cantab Agreements [Member] \| Minimum [Member]
Noncontrolling Interest [Line Items]
Ownership percentage			5.00%
Spero Cantab [Member] \| Pro Bono Bio PLC [Member] \| Cantab Agreements [Member] \| Maximum [Member]
Noncontrolling Interest [Line Items]
Ownership percentage			12.50%
Spero Gyrase, Inc. [Member]
Noncontrolling Interest [Line Items]
Ownership percentage							20.00%
Non-controlling interest	$ 355,000			$ 400,000		$ 355,000	$ 380,000		$ 400,000