Earnings Per Share - Narrative (Details)	Jun. 30, 2021	Dec. 31, 2020
Class B common stock
Reconciliation of the numerators and denominators used in the basic and diluted per-share computations
Ratio for converting shares of Class B common stock into shares of Class A common stock	2,400	2,400

The ratio applied to Class B common stock shares for purposes of determining the number of Class A common stock shares into which the stock will be converted (the number of Class A common stock shares into which one Class B common stock share may be converted).

No definition available.

Name:	erie_CommonStockConversionRatio
Namespace Prefix:	erie_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant