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Condensed Statements of Stockholders' Equity (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2020	Jun. 30, 2020
Common stock, issuance costs		$ 6,626
ATM
Common stock, issuance costs	$ 561

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- Definition

Common stock issuance costs.

+ References

No definition available.

+ Details

Name:	stro_CommonStockIssuanceCosts
Namespace Prefix:	stro_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=stro_AttheMarketIssuanceSalesAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: