Fair Value Measurements (Details 5) - Non-recurring - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Impaired loans
Fair value measurements
Impairment charges (recoveries)	$ 500	$ 0
Partnership investments
Fair value measurements
Impairment charges (recoveries)	0	0
Mortgage servicing rights
Fair value measurements
Impairment charges (recoveries)	0	0
Repossessions
Fair value measurements
Impairment charges (recoveries)	790	580
Other real estate
Fair value measurements
Impairment charges (recoveries)	50	0
Total
Fair value measurements
Impaired loans - collateral based	7,994	6,280
Assets measured at fair value	24,769	21,686
Total \| Partnership investments
Fair value measurements
Accrued income and other assets	1,000	1,032
Total \| Mortgage servicing rights
Fair value measurements
Accrued income and other assets	4,349	4,297
Total \| Repossessions
Fair value measurements
Accrued income and other assets	10,114	9,373
Total \| Other real estate
Fair value measurements
Accrued income and other assets	1,312	704
Level 3
Fair value measurements
Impaired loans - collateral based	7,994	6,280
Assets measured at fair value	24,769	21,686
Level 3 \| Partnership investments
Fair value measurements
Accrued income and other assets	1,000	1,032
Level 3 \| Mortgage servicing rights
Fair value measurements
Accrued income and other assets	4,349	4,297
Level 3 \| Repossessions
Fair value measurements
Accrued income and other assets	10,114	9,373
Level 3 \| Other real estate
Fair value measurements
Accrued income and other assets	$ 1,312	$ 704

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

No definition available.

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Namespace Prefix:	srce_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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

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Namespace Prefix:	srce_
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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

No definition available.

+ Details

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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

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- Details

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