XML 48 R22.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Net Loss per Share | 12 Months Ended
--- | ---
Dec. 31, 2017
Earnings Per Share [Abstract] |
Net Loss per Share | 15. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders of Spero Therapeutics, Inc. was calculated as follows (in thousands, except share and per share amounts):
|  | Year Ended December 31, |  |
|  | 2017 |  |  | 2016 |  |  | 2015 |  |
Numerator: |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss |  | $ | (39,886 | ) |  | $ | (32,641 | ) |  | $ | (13,153 | ) |
Less: Net loss attributable to non-controlling interests |  |  | (1,143 | ) |  |  | (7,150 | ) |  |  | (2,999 | ) |
Plus: Cumulative dividends on redeemable convertible preferred shares |  |  | (6,146 | ) |  |  | (3,441 | ) |  |  | (932 | ) |
Plus: Accretion of bridge units and redeemable convertible preferred shares to redemption value |  |  | (1,208 | ) |  |  | (996 | ) |  |  | (2,341 | ) |
Net loss attributable to common stockholders of Spero Therapeutics, Inc. |  | $ | (46,097 | ) |  | $ | (29,928 | ) |  | $ | (13,427 | ) |
Denominator: |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average common shares outstanding, basic and diluted |  |  | 2,586,865 |  |  |  | 312,169 |  |  |  | 252,807 |  |
Net loss per share attributable to common stockholders of Spero Therapeutics, Inc., basic and diluted |  | $ | (17.82 | ) |  | $ | (95.87 | ) |  | $ | (53.11 | ) |
The Company excluded potentially dilutive securities from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders of Spero Therapeutics, Inc. is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:
|  | December 31, |  |
|  | 2017 |  |  | 2016 |  |  | 2015 |  |
Options to purchase common stock |  |  | 2,011,296 |  |  |  | — |  |  |  | — |  |
Redeemable convertible preferred shares (as converted to common shares) |  |  | — |  |  |  | 2,229,518 |  |  |  | 1,257,213 |  |
Incentive units |  |  | — |  |  |  | 413,266 |  |  |  | 171,758 |  |
|  |  | 2,011,296 |  |  |  | 2,642,784 |  |  |  | 1,428,971 |  |

X
- References No definition available. + Details
Name: | us-gaap_EarningsPerShareAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The entire disclosure for earnings per share. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -URI http://asc.fasb.org/topic&trid=2144383 + Details
Name: | us-gaap_EarningsPerShareTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration