Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Cost of pension plans:
Service cost for benefits earned	$ 13,260	$ 10,873	$ 39,780	$ 32,620
Interest cost on benefits obligation	9,206	9,395	27,618	28,184
Expected return on plan assets	(12,569)	(12,353)	(37,706)	(37,059)
Prior service cost amortization	357	336	1,071	1,007
Net actuarial loss amortization	4,027	3,031	12,080	9,093
Pension plan cost	$ 14,281	$ 11,282	$ 42,843	$ 33,845
Erie Insurance Exchange
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)			58.00%