INCOME TAXES (Schedule of Deferred Tax Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Federal net operating loss carryforwards	$ 185,247	$ 200,139
State net operating loss carryforwards	57,843	66,578
Allowance for loan losses	29,102	35,354
Loans held for sale	1,088	2,341
Alternative minimum and general business tax credits	21,186	20,830
Interest on nonaccrual loans	8,620	9,078
Deferred compensation	4,591	4,070
Core deposit intangibles	2,135	2,493
Partnership and corporate investments	4,520us-gaap_DeferredTaxAssetsInvestments	5,945us-gaap_DeferredTaxAssetsInvestments
Deferred loan charge-offs and other fraud losses	3,847	1,426
Other real estate	13,734	15,893
Accrued contingent liabilities	2,414	1,908
Depreciation on bank premises and equipment	1,796	0
State taxes	0us-gaap_DeferredTaxAssetsStateTaxes	(19,325)us-gaap_DeferredTaxAssetsStateTaxes
Other	11,993us-gaap_DeferredTaxAssetsOther	12,531us-gaap_DeferredTaxAssetsOther
Gross deferred tax assets	348,116us-gaap_DeferredTaxAssetsGross	359,261us-gaap_DeferredTaxAssetsGross
Valuation allowance	(35,541)	(43,380)	(376,224)	(391,629)
Deferred tax assets, net of valuation allowance	312,575us-gaap_DeferredTaxAssetsNet	315,881us-gaap_DeferredTaxAssetsNet
Deferred tax liabilities:
State taxes	17,799fbspra_DeferredTaxLiabilitiesStateTaxes	0fbspra_DeferredTaxLiabilitiesStateTaxes
Servicing rights	4,653	4,655
Net fair value adjustment for available-for-sale investment securities	5,270	1,055
Deferred gain on reclassification of investment securities from available for sale to held to maturity	4,211	4,988
Equity investments	5,681	5,683
Thrift base year tax bad debt reserve	0	10,605
Net deferred loan fees	1,860	1,870
Depreciation on bank premises and equipment	0	(1,561)
Other	1,254us-gaap_DeferredTaxLiabilitiesOther	1,102us-gaap_DeferredTaxLiabilitiesOther
Deferred tax liabilities	40,728us-gaap_DeferredIncomeTaxLiabilities	28,397us-gaap_DeferredIncomeTaxLiabilities
Net deferred tax assets	$ 271,847us-gaap_DeferredTaxAssetsLiabilitiesNet	$ 287,484us-gaap_DeferredTaxAssetsLiabilitiesNet

Deferred Tax Assets, Alternative Minimum and General Business Tax Credits

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Deferred Tax Assets, Interest on Nonaccrual Loans

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Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Deferred Loan Charge-offs and Other Fraud Losses

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Deferred Tax Liabilities, Net Deferred Loan Fees

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible domestic operating loss carryforwards. Excludes state and local operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the provision for loan losses.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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