Regulatory Capital (Bank's Actual Capital Amounts And Ratios) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016	Aug. 11, 2011
Tier I capital (to risk weighted assets) Actual Amount			$ 10,000,000
Consolidated
Total capital (to risk weighted assets) Actual Amount	$ 85,783	$ 72,227
Tier I capital (to risk weighted assets) Actual Amount	77,788	65,105
Common equity tier I capital (to risk-weighted assets) Actual Amount	77,788	65,105
Tier I capital (to average adjusted total assets) Actual Amount	$ 77,788	$ 65,105
Total capital (to risk weighted assets) Actual Ratio	12.74%	11.82%
Tier I capital (to risk weighted assets) Actual Ratio	11.55%	10.66%
Common equity tier I capital (to risk-weighted assets) Actual Ratio	11.55%	10.66%
Tier I capital (to average adjusted total assets) Actual Ratio	9.20%	8.43%
Total capital (to risk weighted assets) Minimum For Capital Adequacy Purposes Amount	$ 53,863	$ 48,874
Tier I capital (to risk weighted assets) Minimum For Capital Adequacy Purposes Amount	40,397	36,655
Common equity tier I capital (to risk-weighted assets) Minimum For Capital Adequacy Purposes Amount	30,298	27,491
Tier I capital (to average adjusted total assets) Minimum For Capital Adequacy Purposes Amount	$ 33,838	$ 30,881
Total capital (to risk weighted assets) Minimum For Capital Adequacy Purposes Ratio	8.00%	8.00%
Tier I capital (to risk weighted assets) Minimum For Capital Adequacy Purposes Ratio	6.00%	6.00%
Common equity tier I capital (to risk-weighted assets) Minimum For Capital Adequacy Purposes Ratio	4.50%	4.50%
Tier I capital (to average adjusted total assets) Minimum For Capital Adequacy Purposes Ratio	4.00%	4.00%
Bank
Total capital (to risk weighted assets) Actual Amount	$ 81,996	$ 69,056
Tier I capital (to risk weighted assets) Actual Amount	74,001	61,934
Common equity tier I capital (to risk-weighted assets) Actual Amount	74,001	61,934
Tier I capital (to average adjusted total assets) Actual Amount	$ 74,001	$ 61,934
Total capital (to risk weighted assets) Actual Ratio	12.19%	11.33%
Tier I capital (to risk weighted assets) Actual Ratio	11.01%	10.16%
Common equity tier I capital (to risk-weighted assets) Actual Ratio	11.01%	10.16%
Tier I capital (to average adjusted total assets) Actual Ratio	8.77%	8.09%
Total capital (to risk weighted assets) Minimum For Capital Adequacy Purposes Amount	$ 53,791	$ 48,748
Tier I capital (to risk weighted assets) Minimum For Capital Adequacy Purposes Amount	40,343	36,561
Common equity tier I capital (to risk-weighted assets) Minimum For Capital Adequacy Purposes Amount	30,258	27,420
Tier I capital (to average adjusted total assets) Minimum For Capital Adequacy Purposes Amount	$ 33,743	$ 30,621
Total capital (to risk weighted assets) Minimum For Capital Adequacy Purposes Ratio	8.00%	8.00%
Tier I capital (to risk weighted assets) Minimum For Capital Adequacy Purposes Ratio	6.00%	6.00%
Common equity tier I capital (to risk-weighted assets) Minimum For Capital Adequacy Purposes Ratio	4.50%	4.50%
Tier I capital (to average adjusted total assets) Minimum For Capital Adequacy Purposes Ratio	4.00%	4.00%
Total capital (to risk weighted assets) Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 67,239	$ 60,934
Tier I capital (to risk weighted assets) Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	53,791	48,748
Common equity tier I capital (to risk-weighted assets) Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	43,705	39,607
Tier I capital (to average adjusted total assets) Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 42,179	$ 38,277
Total capital (to risk weighted assets) Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	10.00%	10.00%
Tier I capital (to risk weighted assets) Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	8.00%	8.00%
Common equity tier I capital (to risk-weighted assets) Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	6.50%	6.50%
Tier I capital (to adjusted total assets) Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	5.00%	5.00%

Represent The Common Equity Tier One Risk Based Capital.

No definition available.

Name:	fsfg_CommonEquityTierOneRiskBasedCapital
Namespace Prefix:	fsfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represent the Common Equity Tier One Risk Based Capital Required For Capital Adequacy.

+ References

No definition available.

+ Details

Name:	fsfg_CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacy
Namespace Prefix:	fsfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represent the Common Equity Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets.

+ References

No definition available.

+ Details

Name:	fsfg_CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	fsfg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represent the Common Equity Tier One Risk Based Capital Required To Be Well Capitalized.

+ References

No definition available.

+ Details

Name:	fsfg_CommonEquityTierOneRiskBasedCapitalRequiredToBeWellCapitalized
Namespace Prefix:	fsfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represent the Common Equity Tier One Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets.

+ References

No definition available.

+ Details

Name:	fsfg_CommonEquityTierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	fsfg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represent the Common Equity Tier One Risk Based Capital To Risk Weighted Assets.

+ References

No definition available.

+ Details

Name:	fsfg_CommonEquityTierOneRiskBasedCapitalToRiskWeightedAssets
Namespace Prefix:	fsfg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of total capital as defined in the regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

+ Details

Name:	us-gaap_Capital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacy
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958570-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Leverage Capital divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Risk Based Capital as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958570-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=us-gaap_ConsolidatedEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=fsfg_BankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: