LOANS AND ALLOWANCE FOR LOAN LOSSES (Details 7) (One-to-four-family residential [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013 contracts	Mar. 31, 2012 contracts
One-to-four-family residential [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	16	12
Recorded Investment	$ 2,396	$ 2,307

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

No definition available.

Name:	fbspra_FinancingReceivableSubsequentDefaultNumberOfContracts
Namespace Prefix:	fbspra_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration