Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Cost of pension plans:
Service cost for benefits earned	$ 8,463	$ 9,513	$ 25,390	$ 28,539
Interest cost on benefits obligation	9,827	8,845	29,480	26,536
Expected return on plan assets	(11,872)	(12,815)	(35,614)	(38,444)
Prior service cost amortization	349	339	1,046	1,015
Net actuarial loss amortization	1,279	3,202	3,835	9,606
Pension plan cost	$ 8,046	$ 9,084	$ 24,137	$ 27,252
Erie Insurance Exchange
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)			59.00%