Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 03, 2021
Document and Entity Information
Document Type	10-Q
Document Transition Report	false
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Entity File Number	0-18082
Entity Registrant Name	GREAT SOUTHERN BANCORP, INC.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	43-1524856
Entity Address, Address Line One	1451 E. Battlefield,
Entity Address, City or Town	Springfield,
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	65804
City Area Code	(417)
Local Phone Number	887-4400
Title of 12(b) Security	Common Stock par value $0.01 per share
Trading Symbol	GSBC
Trading Exchange	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Number of common stock shares outstanding		13,338,563
Entity Central Index Key	0000854560
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false