Fair Value Measurements (Details 5) - Non-recurring - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2022	Dec. 31, 2021
Impaired loans
Fair value measurements
Impairment charges	$ 0
Mortgage servicing rights
Fair value measurements
Impairment recoveries	0
Repossessions
Fair value measurements
Impairment charges	0
Other real estate
Fair value measurements
Impairment charges	0
Total
Fair value measurements
Impaired loans - collateral based	861	$ 571
Assets measured at fair value	5,406	6,103
Total \| Mortgage servicing rights
Fair value measurements
Accrued income and other assets	4,443	4,671
Total \| Repossessions
Fair value measurements
Accrued income and other assets	102	861
Level 3
Fair value measurements
Impaired loans - collateral based	861	571
Assets measured at fair value	5,406	6,103
Level 3 \| Mortgage servicing rights
Fair value measurements
Accrued income and other assets	4,443	4,671
Level 3 \| Repossessions
Fair value measurements
Accrued income and other assets	$ 102	$ 861

Represents the portion of the accrued income and other assets balance sheet assertion valued at fair value.

No definition available.

Name:	source_AccruedIncomeAndOtherAssetsFairValueDisclosure
Namespace Prefix:	source_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of write-up of assets recognized in the income statement. Includes, but is not limited to, gains from tangible assets, intangible assets and goodwill.

+ References

No definition available.

+ Details

Name:	source_AssetImpairmentRecoveries
Namespace Prefix:	source_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents impaired loans receivable based on the fair value of the underlying collateral if repayment is expected solely from the collateral as presented on the statement of financial position which are due the Company as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	source_ImpairedLoansReceivableFairValueDisclosure
Namespace Prefix:	source_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123351718&loc=d3e2420-110228

+ Details

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

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=source_ImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=source_MortgageServicingRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=source_RepossessionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=source_OtherRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: