Revenue - Narrative (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Obligations	Sep. 30, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Indemnity's management fee rate as a percent of direct and affiliated assumed written premiums of the Exchange (percentage)			25.00%
Performance obligations under subscriber's agreement \| Obligations			2
(Decrease) increase in allowance for cancellations \| $	$ (800,000)	$ 0	$ 3,600,000	$ 2,900,000

Change in the estimated allowance to reduce the management fee to its estimated net realizable value to account for the potential of mid-term policy cancellations based on historical cancellation rates.

No definition available.

Name:	erie_RevenueRecognitionManagementFeeReturnedPremiumCancellationAllowance
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration