Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Cost of pension plans:
Service cost for benefits earned	$ 8,464	$ 9,513	$ 16,927	$ 19,026
Interest cost on benefits obligation	9,826	8,845	19,653	17,691
Expected return on plan assets	(11,871)	(12,814)	(23,742)	(25,629)
Prior service cost amortization	348	338	697	676
Net actuarial loss amortization	1,278	3,202	2,556	6,404
Pension plan cost	$ 8,045	$ 9,084	$ 16,091	$ 18,168
Erie Insurance Exchange
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)			58.00%