XML 51 R40.htm IDEA: XBRL DOCUMENT
v3.20.2

Stockholders' Equity - Additional Information (Details) - $ / shares |  | 1 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Oct. 01, 2018 | Aug. 31, 2017 | Jun. 30, 2020 | Feb. 29, 2020 | Dec. 31, 2019 | Oct. 30, 2018
Stockholders Equity [Line Items] |  |  |  |  |  |
Voting rights per share |  |  | one vote per share |  |  |
Preferred stock shares authorized |  |  | 10,000,000 |  | 10,000,000 | 10,000,000
Preferred stock, par value |  |  | $ 0.001 |  | $ 0.001 | $ 0.001
Preferred stock, outstanding |  |  | 0 |  | 0 |
Loan and Security Agreement | Oxford Finance LLC |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |
Issuance of warrants to purchase shares |  |  |  | 54,171 |  |
Loan and Security Agreement | Silicon Valley Bank |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |
Issuance of warrants to purchase shares |  |  |  | 27,086 |  |
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |
Issuance of warrants to purchase shares |  |  |  | 81,257 |  |
Exercise price per share |  |  |  | $ 9.23 |  |
Series E Redeemable Convertible Preferred Stock |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |
Issuance of warrants to purchase shares | 46,359 |  |  |  |  |
Preferred stock, conversion basis | 1-for-0.0275 |  |  |  |  |
Series C Redeemable Convertible Preferred Stock |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |
Issuance of warrants to purchase shares | 25,454 |  |  |  |  |
Preferred stock, conversion basis | 1-for-0.0370 |  |  |  |  |
Cancellation of redeemable convertible preferred warrants | 1,232,220 |  |  |  |  |
Conversion of warrants to purchase of shares of common stock | 687,928 |  |  |  |  |
Oxford Finance LLC and Silicon Valley Bank | Series D Two Redeemable Convertible Preferred Stock | Loan and Security Agreement |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |
Issuance of warrants to purchase shares |  | 682,230 |  |  |  |
Exercise price per share |  | $ 0.6596 |  |  |  |
Oxford Finance LLC and Silicon Valley Bank | Series E Redeemable Convertible Preferred Stock | Loan and Security Agreement |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |
Issuance of warrants to purchase shares |  | 1,682,871 |  |  |  |
Exercise price per share |  | $ 0.2674 |  |  |  |
Term of warrant exercisable |  | 10 years |  |  |  |

X
- Definition Cancellation of redeemable convertible preferred warrants. + References No definition available. + Details
Name: | stro_CancellationOfRedeemableConvertiblePreferredWarrants
Namespace Prefix: | stro_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Class of warrant or right term of warrant. + References No definition available. + Details
Name: | stro_ClassOfWarrantOrRightTermOfWarrant
Namespace Prefix: | stro_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Stockholders equity. + References No definition available. + Details
Name: | stro_StockholdersEquityLineItems
Namespace Prefix: | stro_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Exercise price per share or per unit of warrants or rights outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)(4)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
Name: | us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of securities into which each warrant or right may be converted. For example, but not limited to, each warrant may be converted into two shares. + References No definition available. + Details
Name: | us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
Name: | us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Description of voting rights of common stock. Includes eligibility to vote and votes per share owned. Include also, if any, unusual voting rights. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 + Details
Name: | us-gaap_CommonStockVotingRights
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Describe the conversion features of preferred stock if preferred stock is convertible. That is, shares of preferred stock into which another convertible security was converted, or shares of preferred stock into which another class of preferred stock was converted. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockConversionBasis
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockParOrStatedValuePerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockSharesAuthorized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockSharesOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_TypeOfArrangementAxis=stro_LoanAndSecurityAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=stro_SeriesERedeemableConvertiblePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=us-gaap_SeriesCPreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=stro_OxfordFinanceLimitedLiabilityCompanyAndSiliconValleyBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=stro_SeriesDTwoRedeemableConvertiblePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |