Jointly Owned Utility Plan, Proportionate Ownership Share of Generating Capacity, Megawatts

No definition available.

Name:	opc_JointlyOwnedUtilityPlanProportionateOwnershipShareOfGeneratingCapacityMegawatts
Namespace Prefix:	opc_
Data Type:	dtr-types1:powerItemType
Balance Type:	na
Period Type:	duration

- Definition

Jointly Owned Utility Plan, Total Construction Costs Paid

+ References

No definition available.

+ Details

Name:	opc_JointlyOwnedUtilityPlanTotalConstructionCostsPaid
Namespace Prefix:	opc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Jointly Owned Utility Plant, Proceeds From Settlement Agreement

+ References

No definition available.

+ Details

Name:	opc_JointlyOwnedUtilityPlantProceedsFromSettlementAgreement
Namespace Prefix:	opc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Jointly Owned Utility Plant, Remaining Additional Capital Costs To Be Incurred

+ References

No definition available.

+ Details

Name:	opc_JointlyOwnedUtilityPlantRemainingAdditionalCapitalCostsToBeIncurred
Namespace Prefix:	opc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Nuclear Production Tax Credit

+ References

No definition available.

+ Details

Name:	opc_NuclearProductionTaxCredit
Namespace Prefix:	opc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the number of units constructed in connection with the generation of nuclear energy.

+ References

No definition available.

+ Details

Name:	opc_NumberOfNuclearGeneratingPlants
Namespace Prefix:	opc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 360
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479070/980-360-S99-1

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_PublicUtilityAxis=opc_VogtleUnitsNumber3AndNumber4Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=opc_GeorgiaPowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=opc_EngineeringProcurementAndConstructionAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=opc_WestinghouseElectricCompanyLlcAndStoneWebsterInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=opc_OwnershipParticipationAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=opc_GlobalAmendmentsToTermSheetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=us-gaap_JointlyOwnedNuclearPowerPlantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Vogtle Units No. 3 and No. 4 Construction Project - Narrative (Details) - Vogtle Units No. 3 & No. 4 $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2025 USD ($) unit MW	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Public Utility Property Plant and Equipment
Ownership interest (as a percent)	30.00%
Georgia Power
Public Utility Property Plant and Equipment
Nuclear production tax credit	$ 24,424	$ 72,600	$ 21,700
EPC Agreement \| Westinghouse Electric Company LLC and Stone & Webster, Inc.
Public Utility Property Plant and Equipment
Number of nuclear units \| unit	2
Ownership participation agreement
Public Utility Property Plant and Equipment
Ownership share, generating capacity (in megawatts) \| MW	727
Total construction costs paid	$ 8,300,000
Proceeds from settlement agreement	1,100,000
Ownership participation agreement \| Minimum
Public Utility Property Plant and Equipment
Additional capital costs incurred	10,000
Ownership participation agreement \| Maximum
Public Utility Property Plant and Equipment
Additional capital costs incurred	15,000
Global Amendments to Term Sheet \| Jointly Owned Nuclear Power Plant \| Georgia Power
Public Utility Property Plant and Equipment
Total construction costs paid	$ 437,000