Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cost of pension plans:
Service cost for benefits earned	$ 10,873	$ 8,463
Interest cost on benefits obligation	9,395	9,827
Expected return on plan assets	(12,353)	(11,871)
Prior service cost amortization	336	349
Net actuarial loss amortization	3,031	1,278
Pension plan cost	$ 11,282	$ 8,046
Erie Insurance Exchange
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)	57.00%