Accounting Policies (Details)	3 Months Ended
Mar. 31, 2022
Minimum
Summary of Significant Accounting Policies [Line Items]
Period of sustained performance required to change from non-performing to performing status	6 months

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

No definition available.

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