Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Mar. 09, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Entity Registrant Name	SOUTHWEST BANCORP INC
Entity Central Index Key	0000914374
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Amendment Flag	false
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Trading Symbol	oksb
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 297.0
Entity Common Stock, Shares Outstanding		18,689,022
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes