Document and Entity Information	3 Months Ended
	Mar. 31, 2018 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	Mar. 31, 2018
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	2018
Document Fiscal Period Focus	Q1