Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Cost of pension plans:
Service cost for benefits earned	$ 10,874	$ 8,464	$ 21,747	$ 16,927
Interest cost on benefits obligation	9,394	9,826	18,789	19,653
Expected return on plan assets	(12,353)	(11,871)	(24,706)	(23,742)
Prior service cost amortization	335	348	671	697
Net actuarial loss amortization	3,031	1,278	6,062	2,556
Pension plan cost	$ 11,281	$ 8,045	$ 22,563	$ 16,091
Erie Insurance Exchange
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)			58.00%