Revenue - Narrative (Details)	9 Months Ended
Sep. 30, 2019 Obligations
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	2

Number of performance obligations recognized by Indemnity acting as attorney-in-fact for the subscribers of the Exchange in accordance with Topic 606.

No definition available.

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Namespace Prefix:	erie_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration