Postretirement Benefits - Cost of Pension Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cost of pension plans:
Service cost for benefits earned	$ 53,041	$ 43,492	$ 33,854
Interest cost on benefit obligation	36,824	37,578	39,306
Expected return on plan assets	(50,275)	(49,411)	(47,484)
Prior service cost amortization	1,428	1,343	1,394
Net actuarial loss amortization	16,106	12,125	5,113
Pension plan cost	$ 57,124	$ 45,127	$ 32,183
Erie Insurance Exchange (EIE)
Postretirement benefits
Postretirement annual benefit expense reimbursed to Indemnity from the exchange and its subsidiaries	58.00%