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Accounting Policies (Details)	9 Months Ended
	Sep. 30, 2025
Minimum
Summary of Significant Accounting Policies [Line Items]
Period of sustained performance required to change from non-performing to performing status	6 months

X

- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

Name:	source_SummaryOfSignificantAccountingPoliciesLineItems
Namespace Prefix:	source_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Represents the period of sustained performance required to change loan from non-performing to performing.

+ References

No definition available.

+ Details

Name:	source_SustainedPerformancePeriodRequiredForPerformingStatus
Namespace Prefix:	source_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Details

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