Actual Loss Period

No definition available.

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- Definition

Concentration risk credit risk financial instrument percentage.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable Purchase Credit Impaired

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Interest And Fee Income Nonaccruing Loans

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Loans and Debt Securities Acquired with Deteriorated Credit Quality, Discount

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loans Purchased Evaluated in Conjunction With The Acquisition

+ References

No definition available.

+ Details

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

- Definition

Loans Purchased Evaluated in Conjunction With The Acquisition, Discount

+ References

No definition available.

+ Details

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Namespace Prefix:	oksb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number Of Days For Independent Appraisals On Real Estate Collateral

+ References

No definition available.

+ Details

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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

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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

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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

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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=84176398&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=65878427&loc=d3e1107-107759

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=64827811&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=65878427&loc=SL51721533-107759

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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=77997519&loc=d3e13537-108611

+ Details

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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=82895541&loc=d3e18794-111554

+ Details

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

- Details

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- Details

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- Details

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Loans And Allowance For Loan Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Oct. 09, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 6.0	$ 6.0	$ 4.4
Actual loss period		3 years
Period to sell loans from the date of closing		1 month
Loans Purchased Evaluated in Conjunction With The Acquisition				$ 200.0
Loans Purchased Evaluated in Conjunction With The Acquisition, Discount				4.5
Loans, purchase credit impaired				7.8
Loans and debt securities acquired with deteriorated credit quality, discount				$ 3.3
Accrued additional interest income		$ 0.5
Interest And Fee Income Nonaccruing Loans		$ 0.2
Troubled debt restructuring default period		90 days
Troubled debt restructuring Period		12 months
Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to individuals and businesses	$ 662.6
Percentage of loans to individuals and businesses	34.00%	34.00%
Real Estate Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal of mortgage loans serviced for others	$ 463.8	$ 463.8	$ 460.6
Healthcare [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to individuals and businesses	$ 429.5
Percentage of loans to individuals and businesses	22.00%	22.00%
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of days for independent appraisals on real estate collateral		30 days