Agreement termination notice period.

No definition available.

Name:	sldb_AgreementTerminationNoticePeriod
Namespace Prefix:	sldb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Issuance of common stock to related party in connection with stock purchase agreement.

+ References

No definition available.

+ Details

Name:	sldb_IssuanceOfCommonStockToRelatedPartyInConnectionWithStockPurchaseAgreement
Namespace Prefix:	sldb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Milestone payments upon achievement of development milestone.

+ References

No definition available.

+ Details

Name:	sldb_MilestonePaymentsUponAchievementOfDevelopmentMilestone
Namespace Prefix:	sldb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Milestone payments upon achievement of net sales milestones.

+ References

No definition available.

+ Details

Name:	sldb_MilestonePaymentsUponAchievementOfNetSalesMilestones
Namespace Prefix:	sldb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Milestone payments upon achievement of regulatory milestone.

+ References

No definition available.

+ Details

Name:	sldb_MilestonePaymentsUponAchievementOfRegulatoryMilestone
Namespace Prefix:	sldb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of net income and net losses on net sales.

+ References

No definition available.

+ Details

Name:	sldb_PercentageOfNetIncomeAndNetLossesOnNetSales
Namespace Prefix:	sldb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of option to fund of development cost.

+ References

No definition available.

+ Details

Name:	sldb_PercentageOfOptionToFundOfDevelopmentCost
Namespace Prefix:	sldb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of outstanding common stock.

+ References

No definition available.

+ Details

Name:	sldb_PercentageOfOutstandingCommonStock
Namespace Prefix:	sldb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Transaction price.

+ References

No definition available.

+ Details

Name:	sldb_TransactionPrice
Namespace Prefix:	sldb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer.

+ 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.(k)(1))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3(a)(2))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

+ Details

Name:	us-gaap_AccountsReceivableRelatedPartiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130532-203044

+ Details

Name:	us-gaap_ContractWithCustomerLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Cash received from collaborators during the current period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585

+ Details

Name:	us-gaap_ProceedsFromCollaborators
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=120401555&loc=SL114874292-224272

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

+ Details

Name:	us-gaap_RevenueFromRelatedParties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Per share or per unit amount of equity securities issued.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesIssuedPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_CounterpartyNameAxis=sldb_UltragenyxMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=us-gaap_CollaborativeArrangementTransactionWithPartyToCollaborativeArrangementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Collaborations - Additional Information (Detail) - USD ($)		3 Months Ended	6 Months Ended
	Oct. 22, 2020	Jun. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from issuance of common stock			$ 134,878,000
Related party revenue recognized		$ 3,594,000	6,929,000
Related party collaboration receivables		286,000	286,000
Ultragenyx [Member] \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of regulatory milestone			$ 65,000,000
Percentage of option to fund of development cost			30.00%
Percentage of net income and net losses on net sales			30.00%
Agreement termination notice period			90 days
Issued and sold shares of common stock	7,825,797
Common stock issued price per share	$ 5.1113
Proceeds from issuance of common stock	$ 40,000,000
Percentage of outstanding common stock	14.45%
Proceeds from equity investment under stock purchase agreement			$ 22,513,000
Transaction price			0
Related party revenue recognized		3,594,000	6,929,000
Proceeds from collaborators		280,000	280,000
Deferred revenue - related party		14,354,000	14,354,000	$ 17,663,000	$ 20,718,000	$ 14,354,000
Related party collaboration receivables		$ 286,000	286,000	$ 280,000		$ 286,000
Maximum [Member] \| Ultragenyx [Member] \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of development milestone			25,000,000
Milestone Payments upon achievement of net sales milestones			$ 165,000,000
Percentage of outstanding common stock			10.00%
Minimum [Member] \| Ultragenyx [Member] \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of outstanding common stock			10.00%