Actual Loss Period

No definition available.

Name:	oksb_ActualLossPeriod
Namespace Prefix:	oksb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Concentration risk credit risk financial instrument percentage.

+ References

No definition available.

+ Details

Name:	oksb_ConcentrationRiskCreditRiskFinancialInstrumentPercentage
Namespace Prefix:	oksb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Covered assets reimbursement ratio.

+ References

No definition available.

+ Details

Name:	oksb_CoveredAssetsReimbursementRatio
Namespace Prefix:	oksb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Cumulative charge offs against noncovered nonaccrual loan.

+ References

No definition available.

+ Details

Name:	oksb_CumulativeChargeOffsAgainstNoncoveredNonaccrualLoan
Namespace Prefix:	oksb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Loans and lease receivable allowance.

+ References

No definition available.

+ Details

Name:	oksb_LoansAndLeaseReceivableAllowance
Namespace Prefix:	oksb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number Of Collateral Dependent Lending Relationships

+ References

No definition available.

+ Details

Name:	oksb_NumberOfCollateralDependentLendingRelationships
Namespace Prefix:	oksb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number Of Days For Independent Appraisals On Real Estate Collateral

+ References

No definition available.

+ Details

Name:	oksb_NumberOfDaysForIndependentAppraisalsOnRealEstateCollateral
Namespace Prefix:	oksb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period to sell loans from the date of closing.

+ References

No definition available.

+ Details

Name:	oksb_PeriodToSellLoansFromDateOfClosing
Namespace Prefix:	oksb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Troubled debt restructuring period.

+ References

No definition available.

+ Details

Name:	oksb_TroubledDebtRestructuringPeriod
Namespace Prefix:	oksb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Unpaid principal balance of mortgage loans serviced for others.

+ References

No definition available.

+ Details

Name:	oksb_UnpaidPrincipalOfMortgageLoansServicedForOthers
Namespace Prefix:	oksb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Definition

Represents the sum of the carrying value of all the Assets Held-for-Sale at the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

+ Details

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

- Definition

Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskCreditRiskFinancialInstrumentMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This is the result of the principal amount outstanding of total loans managed or securitized less securitized loans and loans that are in the process of being securitized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=13989330&loc=d3e107314-111719

+ Details

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

Loans And Allowance For Loan Losses (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended			3 Months Ended
	Mar. 31, 2014 contract	Dec. 31, 2013 contract	Mar. 31, 2014 Real Estate Mortgage [Member]	Mar. 31, 2013 Real Estate Mortgage [Member]	Mar. 31, 2014 Commercial Real Estate [Member] contract	Mar. 31, 2014 Maximum [Member]	Mar. 31, 2014 Noncovered [Member]	Dec. 31, 2013 Noncovered [Member]	Jun. 19, 2009 Covered [Member] Maximum [Member]	Jun. 19, 2009 Covered [Member] Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reimbursement Ratio									95.00%	80.00%
Principal balances							$ 12.4	$ 14.6
Impairment reserves							2.8	2.9
Loans to individuals and businesses	420.3
Percentage of loans to individuals and businesses	32.00%
Number of days for independent appraisals on real estate collateral						30 days
Number of collateral dependent lending relationships	7	5			4
Loans held for sale	5.7	3.1
Actual loss period	3 years
Period to sell loans from the date of closing	1 month
Unpaid principal of mortgage loans serviced for others			391.3	390.7
Accrued additional interest income	0.2
Cumulative charge-offs against noncovered nonaccrual loans	$ 5.5	$ 8.2
Troubled debt restructuring Period	12 months