Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cost of pension plans:
Service cost for benefits earned	$ 13,260	$ 10,873
Interest cost on benefits obligation	9,206	9,395
Expected return on plan assets	(12,569)	(12,353)
Prior service cost amortization	357	336
Net actuarial loss amortization	4,027	3,031
Pension plan cost	$ 14,281	$ 11,282
Erie Insurance Exchange
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)	58.00%