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 with maturities greater than three years, but less than four years.

No definition available.

Name:	bsf_InterestBearingTimeDepositsInBanksInterestRateMaturitiesYearFour
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 one year, but less than three years.

No definition available.

Name:	bsf_InterestBearingTimeDepositsInBanksInterestRateMaturitiesYearTwo
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 greater than three years, butless than four years.

No definition available.

Name:	bsf_InterestBearingTimeDepositsInBanksWeightedAverageInterestRateMaturitiesYearFour
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 one year, but two years or less.

No definition available.

Name:	bsf_InterestBearingTimeDepositsInBanksWeightedAverageInterestRateMaturitiesYearTwo
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.