LOANS AND ALLOWANCE FOR LOAN LOSSES (Aging of Loans by Loan Classification) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	$ 5,442	$ 8,475
60-89 Days	1,837	4,424
Recorded Investment Greater Than 90 Days Accruing	163	424
Nonaccrual	57,476	52,956
Total Past Due	64,918	66,279
Current	3,084,325	2,790,816
Total loans	3,149,243	2,857,095	2,930,747
Commercial, financial and agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	132	447
60-89 Days	430	394
Recorded Investment Greater Than 90 Days Accruing	54	80
Nonaccrual	9,486	10,523
Total Past Due	10,102	11,444
Current	685,165	589,260
Total loans	695,267	600,704
Real estate construction and development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	431	0
60-89 Days	0	0
Recorded Investment Greater Than 90 Days Accruing	0	0
Nonaccrual	3,393	4,914
Total Past Due	3,824	4,914
Current	86,027	116,748
Total loans	89,851	121,662
Residential mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	2,690	4,262
60-89 Days	986	2,637
Recorded Investment Greater Than 90 Days Accruing	35	162
Nonaccrual	13,890	20,063
Total Past Due	17,601	27,124
Current	603,567	545,040
Total loans	621,168	572,164
Home equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	1,857	2,256
60-89 Days	334	963
Recorded Investment Greater Than 90 Days Accruing	72	182
Nonaccrual	6,831	7,361
Total Past Due	9,094	10,762
Current	386,448	338,562
Total loans	395,542	349,324
Multi-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	0	0
60-89 Days	0	0
Recorded Investment Greater Than 90 Days Accruing	0	0
Nonaccrual	19,731	1,793
Total Past Due	19,731	1,793
Current	95,703	119,511
Total loans	115,434	121,304
Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	196	1,423
60-89 Days	54	391
Recorded Investment Greater Than 90 Days Accruing	0	0
Nonaccrual	4,122	8,283
Total Past Due	4,372	10,097
Current	1,178,670	1,038,137
Total loans	1,183,042	1,048,234
Consumer and installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	136	87
60-89 Days	33	39
Recorded Investment Greater Than 90 Days Accruing	2	0
Nonaccrual	23	19
Total Past Due	194	145
Current	17,334	18,010
Total loans	17,528	18,155
Loans held for sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days	0	0
60-89 Days	0	0
Recorded Investment Greater Than 90 Days Accruing	0	0
Nonaccrual	0	0
Total Past Due	0	0
Current	31,411	25,548
Total loans	$ 31,411	$ 25,548

Financing receivables that are less than 60 days past due but more than 29 days past due.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are less than 90 days past due but more than 59 days past due.

+ References

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are current.

+ References

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbspra_CommercialFinancialAndAgriculturalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbspra_LoansHeldForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbspra_MultiFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbspra_RealEstateConstructionAndDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: