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v3.20.2

Related-Party Transactions - Additional Information (Details) - Maximum [Member] | Jun. 16, 2020 | May 14, 2020
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Merck | Sutro Biopharma |  |
Related Party Transaction [Line Items] |  |
Equity interest percentage |  | 10.00%
Vaxcyte, Inc. |  |
Related Party Transaction [Line Items] |  |
Percentage common stock ownership interest | 4.00% |

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- Definition Common stock ownership percentage. + References No definition available. + Details
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Namespace Prefix: | stro_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=stro_MerckSharpAndDohmeCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_OwnershipAxis=stro_SutroBiopharmaINCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=stro_VaxcyteIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |