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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Maximum received fund amount.

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Number of option period for funding from government contract.

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Proceeds from government contract

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Upfront payments.

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

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The cash outflow to reacquire common stock during the period.

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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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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			12 Months Ended
	Dec. 31, 2017 USD ($) Option	Jul. 31, 2017 USD ($)	Jun. 30, 2016 USD ($) Option shares	Dec. 31, 2017 USD ($) Option	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Noncontrolling Interest [Line Items]
Research and development expense				$ 32,869,000	$ 26,333,000	$ 11,125,000
Non-controlling interest	$ 355,000			355,000	$ (3,808,000)
Spero Cantab [Member]
Noncontrolling Interest [Line Items]
Ownership percentage					12.50%
Non-controlling interest	0			0	$ 1,303,000
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]
Maximum potential funding from government contract			$ 5,700,000
Number of option period for funding from government contract \| Option			3
Maximum received fund	$ 1,300,000			$ 1,300,000
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 \| Option	2			2
Committed amount from government contract	$ 5,100,000			$ 5,100,000
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%