Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Cost of pension plans:
Service cost for benefits earned	$ 10,873	$ 8,463	$ 32,620	$ 25,390
Interest cost on benefits obligation	9,395	9,827	28,184	29,480
Expected return on plan assets	(12,353)	(11,872)	(37,059)	(35,614)
Prior service cost amortization	336	349	1,007	1,046
Net actuarial loss amortization	3,031	1,279	9,093	3,835
Pension plan cost	$ 11,282	$ 8,046	$ 33,845	$ 24,137
Erie Insurance Exchange
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)			58.00%