Loan and Lease Financings (Details)	6 Months Ended
Jun. 30, 2016 USD ($) item	Dec. 31, 2015 USD ($)
Receivables [Abstract]
Number of methods to assess credit risk \| item	2
Loan and Lease Financings
Recorded investment in loans and leases	$ 4,152,763,000	$ 3,994,692,000
Loan and lease financings excluding residential real estate and consumer loans
Loan and Lease Financings
Recorded investment in loans and leases	3,513,563,000	3,382,084,000
Commercial and agricultural
Loan and Lease Financings
Recorded investment in loans and leases	759,175,000	744,749,000
Auto and light truck
Loan and Lease Financings
Recorded investment in loans and leases	457,586,000	425,236,000
Medium and heavy duty truck
Loan and Lease Financings
Recorded investment in loans and leases	273,674,000	278,254,000
Aircraft
Loan and Lease Financings
Recorded investment in loans and leases	822,842,000	778,012,000
Construction equipment
Loan and Lease Financings
Recorded investment in loans and leases	484,354,000	455,565,000
Commercial real estate
Loan and Lease Financings
Recorded investment in loans and leases	715,932,000	700,268,000
Credit Quality Grades 1-6 \| Loan and lease financings excluding residential real estate and consumer loans
Loan and Lease Financings
Recorded investment in loans and leases	3,400,643,000	3,278,484,000
Credit Quality Grades 1-6 \| Commercial and agricultural
Loan and Lease Financings
Recorded investment in loans and leases	725,345,000	710,030,000
Credit Quality Grades 1-6 \| Auto and light truck
Loan and Lease Financings
Recorded investment in loans and leases	427,067,000	413,836,000
Credit Quality Grades 1-6 \| Medium and heavy duty truck
Loan and Lease Financings
Recorded investment in loans and leases	271,809,000	275,367,000
Credit Quality Grades 1-6 \| Aircraft
Loan and Lease Financings
Recorded investment in loans and leases	792,536,000	750,264,000
Credit Quality Grades 1-6 \| Construction equipment
Loan and Lease Financings
Recorded investment in loans and leases	479,698,000	448,683,000
Credit Quality Grades 1-6 \| Commercial real estate
Loan and Lease Financings
Recorded investment in loans and leases	704,188,000	680,304,000
Credit Quality Grades 7-12
Loan and Lease Financings
Relationships reviewed quarterly as part of management's evaluation of the appropriateness of the reserve for loan and lease losses	100,000
Credit Quality Grades 7-12 \| Loan and lease financings excluding residential real estate and consumer loans
Loan and Lease Financings
Recorded investment in loans and leases	112,920,000	103,600,000
Credit Quality Grades 7-12 \| Commercial and agricultural
Loan and Lease Financings
Recorded investment in loans and leases	33,830,000	34,719,000
Credit Quality Grades 7-12 \| Auto and light truck
Loan and Lease Financings
Recorded investment in loans and leases	30,519,000	11,400,000
Credit Quality Grades 7-12 \| Medium and heavy duty truck
Loan and Lease Financings
Recorded investment in loans and leases	1,865,000	2,887,000
Credit Quality Grades 7-12 \| Aircraft
Loan and Lease Financings
Recorded investment in loans and leases	30,306,000	27,748,000
Credit Quality Grades 7-12 \| Construction equipment
Loan and Lease Financings
Recorded investment in loans and leases	4,656,000	6,882,000
Credit Quality Grades 7-12 \| Commercial real estate
Loan and Lease Financings
Recorded investment in loans and leases	$ 11,744,000	$ 19,964,000

Represents the amount of loans and leases where the internal credit quality grade is at or below a predetermined classification which are included in comprehensive analysis.

No definition available.

+ Details

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

- Definition

Represents the number of methods to assess credit risk of loans and leases receivables.

+ References

No definition available.

+ Details

Name:	srce_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk
Namespace Prefix:	srce_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- 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_FinancingReceivableRecordedInvestmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5074-111524

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=srce_GroupOfLoansOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=srce_CommercialAndAgriculturalLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=srce_AutoAndLightTruckMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=srce_MediumAndHeavyDutyTruckMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=srce_AircraftFinancingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=srce_ConstructionEquipmentFinancingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=srce_InternallyAssignedGrade1To6Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=srce_InternallyAssignedGrade7To12Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: