Postretirement Benefits - Cost of Pension Plans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) participant
Cost of pension plans:
Service cost for benefits earned	$ 33,854	$ 38,052	$ 31,106
Interest cost on benefit obligation	39,306	35,382	34,275
Expected return on plan assets	(47,484)	(51,260)	(41,267)
Prior service cost amortization	1,394	1,353	871
Net actuarial loss amortization	5,113	12,809	9,301
Settlement cost	0	0	302
Pension plan cost	$ 32,183	$ 36,336	$ 34,588
Erie Insurance Exchange (EIE)
Postretirement benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)	59.00%
Nonqualified Plan | Supplemental employee retirement plan (SERP) | Unfunded plan
Cost of pension plans:
Number of former plan participants resulting in charges recognized as settlements | participant			2