Mortgage Servicing Rights (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Expected amortization expense on mortgage servicing rights
2018	$ 660
2019	570
2020	490
2021	420
2022	360
Residential mortgage loans
Mortgage Servicing Rights
Unpaid principal balance	$ 752,990	$ 761,850	$ 798,510

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

No definition available.

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Namespace Prefix:	srce_
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- Definition

Represents the amount of expense to be charged against earnings in the next fiscal year following the latest balance sheet date, for the periodic recognition of servicing assets relative to estimated net servicing income.

+ References

No definition available.

+ Details

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Namespace Prefix:	srce_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Represents the amount of expense to be charged against earnings in the year five following the latest balance sheet date, for the periodic recognition of servicing assets relative to estimated net servicing income.

+ References

No definition available.

+ Details

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Namespace Prefix:	srce_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of expense to be charged against earnings in the year four following the latest balance sheet date, for the periodic recognition of servicing assets relative to estimated net servicing income.

+ References

No definition available.

+ Details

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Namespace Prefix:	srce_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Represents the amount of expense to be charged against earnings in the year three following the latest balance sheet date, for the periodic recognition of servicing assets relative to estimated net servicing income.

+ References

No definition available.

+ Details

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Namespace Prefix:	srce_
Data Type:	xbrli:monetaryItemType
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- Definition

Represents the amount of expense to be charged against earnings in the year two following the latest balance sheet date, for the periodic recognition of servicing assets relative to estimated net servicing income.

+ References

No definition available.

+ Details

Name:	srce_ServicingAssetAtAmortizedValueExpectedAmortizationInYearTwo
Namespace Prefix:	srce_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This is the result of the principal amount outstanding of total loans managed or securitized less securitized loans and loans that are in the process of being securitized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

+ Details

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- 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

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- Details

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