Revenue (Details)	6 Months Ended
Jun. 30, 2018
Revenue, Performance Obligation [Abstract]
Indemnity's management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)	25.00%
Number of performance obligations recognized by Indemnity acting as attorney-in-fact for the subscribers of the Exchange	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.

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