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

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 default period

+ References

No definition available.

+ Details

Name:	oksb_TroubledDebtRestructuringDefaultPeriod
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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Amount classified as assets attributable to disposal group held for sale or disposed of.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=51719941&loc=d3e2941-110230

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 45

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=51716988&loc=d3e1107-107759

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 5B

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721673-107760

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=51716988&loc=SL51721533-107759

+ Details

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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=49121117&loc=d3e13537-108611

+ Details

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

- Definition

Amount of allowance for loan and lease losses covered by loss sharing agreements.

+ References

No definition available.

+ Details

Name:	us-gaap_LoansAndLeasesReceivableAllowanceCovered
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

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

- Details

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

- Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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- Details

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Loans And Allowance For Loan Losses (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Jun. 19, 2009
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: Allowance for loan losses, covered			$ (35.0)
Loans held for sale	$ 6.7	$ 1.5
Actual loss period	3 years
Period to sell loans from the date of closing	1 month
Accrued additional interest income	$ 0.3
Troubled debt restructuring default period	90 days
Troubled debt restructuring Period	12 months
Real Estate Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal of mortgage loans serviced for others	$ 416.0	$ 410.3
Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to individuals and businesses	$ 485.7
Percentage of loans to individuals and businesses	34.00%
Healthcare [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to individuals and businesses	$ 422.3
Percentage of loans to individuals and businesses	29.00%
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of days for independent appraisals on real estate collateral	30 days
Covered [Member] \| Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reimbursement Ratio			95.00%
Covered [Member] \| Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reimbursement Ratio			80.00%