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Quarterly Financial Data (Tables) | 12 Months Ended
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Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract] |
Quarterly Financial Information |
|  | March 31, 2017 |  |  | June 30, 2017 |  |  | September 30, 2017 |  |  | December 31, 2017 |
Grant revenue |  | $ | 140 |  |  | $ | 249 |  |  | $ | 597 |  |  | $ | 993 |
Operating expenses |  |  | 7,739 |  |  |  | 10,414 |  |  |  | 10,563 |  |  |  | 14,993 |
Net loss and comprehensive loss |  |  | (6,411 | ) |  |  | (9,763 | ) |  |  | (9,844 | ) |  |  | (13,868 | )
Net loss attributable to Spero Therapeutics, Inc. |  |  | (5,876 | ) |  |  | (9,169 | ) |  |  | (9,836 | ) |  |  | (13,862 | )
Net loss attributable to common shareholders of Spero Therapeutics, Inc. |  |  | (7,130 | ) |  |  | (12,121 | ) |  |  | (12,076 | ) |  |  | (14,770 | )
Net loss per share attributable to common shareholders per share, basic and diluted |  | $ | (21.60 | ) |  | $ | (36.21 | ) |  | $ | (36.02 | ) |  | $ | (1.59 | )
Weighted average shares outstanding, basic and diluted: |  |  | 330,075 |  |  |  | 334,788 |  |  |  | 335,285 |  |  |  | 9,273,783 |
|  | March 31, 2016 |  |  | June 30, 2016 |  |  | September 30, 2016 |  |  | December 31, 2016 |
Grant Revenue |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 335 |
Operating expenses |  |  | 8,417 |  |  |  | 8,080 |  |  |  | 7,914 |  |  |  | 9,145 |
Net loss and comprehensive loss |  |  | (8,430 | ) |  |  | (8,096 | ) |  |  | (7,918 | ) |  |  | (8,197 | )
Net loss attributable to Spero Therapeutics, Inc. |  |  | (5,905 | ) |  |  | (6,059 | ) |  |  | (6,316 | ) |  |  | (7,211 | )
Net loss attributable to common shareholders of Spero Therapeutics, Inc. |  |  | (6,257 | ) |  |  | (7,928 | ) |  |  | (7,410 | ) |  |  | (8,333 | )
Net loss per share attributable to common shareholders per share, basic and diluted |  | $ | (21.51 | ) |  | $ | (25.30 | ) |  | $ | (23.23 | ) |  | $ | (25.68 | )
Weighted average shares outstanding, basic and diluted: |  |  | 290,884 |  |  |  | 313,414 |  |  |  | 318,948 |  |  |  | 324,521 |

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- Definition Tabular disclosure of quarterly financial data. Includes, but is not limited to, financial information for fiscal quarters, cumulative effect of a change in accounting principle and earnings per share data. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a)-(j) -URI http://asc.fasb.org/extlink&oid=84173487&loc=d3e1280-108306 + Details
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