Real Estate Development and Construction (Additional Information) (Detail) (USD $)	3 Months Ended	6 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Real Estate Properties [Line Items]
Development cost cash paid			$ 7,500,000us-gaap_DevelopmentCosts
Expected total development costs			7,700,000fsfg_EstimatedDevelopmentCosts
Depreciation	$ 49,000us-gaap_Depreciation	$ 47,000us-gaap_Depreciation	$ 98,000us-gaap_Depreciation	$ 94,000us-gaap_Depreciation

The capitalized costs incurred during the period (excluded from amortization) to obtain access to proved reserves and to provide facilities for extracting, treating, gathering and storing the oil and gas.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-10.(c)(7)(ii))

-URI http://asc.fasb.org/extlink&oid=27015464&loc=d3e511914-122862

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 10

-Paragraph c

-Subparagraph 3(ii)(A)

-Article 4

Name:	us-gaap_DevelopmentCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration