Document and Entity Information	9 Months Ended
	Sep. 30, 2019 shares
Document and Entity Information
Entity Registrant Name	OGLETHORPE POWER CORP
Document Type	10-Q
Document Period End Date	Sep. 30, 2019
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	0
Entity Central Index Key	0000788816
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false