Document and Entity Information	9 Months Ended
	Sep. 30, 2017 shares
Document and Entity Information Abstract
Entity Registrant Name	OGLETHORPE POWER CORP
Entity Central Index Key	0000788816
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding	0
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3