Postretirement Benefits (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Cost of pension plans:
Service cost for benefits earned		$ 8,463	$ 9,513
Interest cost on benefits obligation		9,827	8,846
Expected return on plan assets		(11,871)	(12,815)
Prior service cost amortization		349	338
Net actuarial loss amortization		1,278	3,202
Pension plan cost	[1]	$ 8,046	$ 9,084
Erie Insurance Exchange
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)		59.00%

[1] The components of pension plan costs other than the service cost component are included in the line item "Other income" in the Statements of Operations after reimbursements from the Exchange and its subsidiaries.