Name:	bsf_InterestBearingTimeDepositsInBanks
Namespace Prefix:	bsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of interest bearing time deposits held by other institutions with maturities greater than four years, but five years or less.

No definition available.

Name:	bsf_InterestBearingTimeDepositsInBanksInterestRateMaturitiesYearFive
Namespace Prefix:	bsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of interest bearing time deposits held by other institutions maturing in the next fiscal year following the latest fiscal year.

No definition available.

Name:	bsf_InterestBearingTimeDepositsInBanksInterestRateMaturitiesYearOne
Namespace Prefix:	bsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of interest bearing time deposits held by other institutions with maturities greater than two years year, but three years or less.

No definition available.

Name:	bsf_InterestBearingTimeDepositsInBanksInterestRateMaturitiesYearThree
Namespace Prefix:	bsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Weighted average interest rate for interest bearing time deposits held by other institutions with maturities greater than four years, but five years or less.

No definition available.

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

Weighted average interest rate for interest bearing time deposits held by other institutions with maturities of one year or less.

No definition available.

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

Weighted average interest rate for interest bearing time deposits held by other institutions with maturities greater than two years, but three years or less.

No definition available.

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

Weighted average interest rate for time deposits held by the entity.

No definition available.