Note 12 - Other Borrowings (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($)
Note 12 - Other Borrowings (Details) [Line Items]
Federal Home Loan Bank Advances, Letter of Credit Disclosures, Maximum Amount Available (in Dollars)	$ 56.6
Notes Payable, Fixed Charge Coverage Ratio	2.0
Notes Payable, Maximum Loan to Value Ratio	75.00%
Notes Payable, Maximum Classified Asset Ratio	50.00%
Notes Payable, Tier 1 Leverage Ratio	8.00%
Maturing in the First Quarter of 2016 [Member]
Note 12 - Other Borrowings (Details) [Line Items]
Federal Home Loan Bank Advances, Letter of Credit Disclosures, Maximum Amount Available (in Dollars)	$ 31.6
Maturing in the Fourth Quarter of 2017 [Member]
Note 12 - Other Borrowings (Details) [Line Items]
Federal Home Loan Bank Advances, Letter of Credit Disclosures, Maximum Amount Available (in Dollars)	$ 25.0

Amount of maximum potential advances or credit available related to letters of credit from the Federal Home Loan Bank (FHLB).

No definition available.

Name:	bsf_FederalHomeLoanBankAdvancesLetterOfCreditDisclosuresMaximumAmountAvailable
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

No definition available.

Name:	bsf_Note12OtherBorrowingsDetailsLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the fixed charge coverage ratio required for the notes payable.

No definition available.

Name:	bsf_NotesPayableFixedChargeCoverageRatio
Namespace Prefix:	bsf_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

Represents the maximum classified asset ratio which is a requirement for the notes payable.

No definition available.

Name:	bsf_NotesPayableMaximumClassifiedAssetRatio
Namespace Prefix:	bsf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the maximum loan to value ratio required for the notes payable.

No definition available.

Name:	bsf_NotesPayableMaximumLoanToValueRatio
Namespace Prefix:	bsf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the Tier 1 leverage ratio required for the notes payable.

No definition available.

Name:	bsf_NotesPayableTier1LeverageRatio
Namespace Prefix:	bsf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Name:	us-gaap_CreditFacilityAxis=bsf_MaturingInTheFirstQuarterOf2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditFacilityAxis=bsf_MaturingInTheFourthQuarterOf2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: