Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Cost of pension plans:
Service cost for benefits earned	$ 9,513	$ 7,777		$ 28,539	$ 23,330
Interest cost on benefits obligation	8,845	8,569		26,536	25,706
Expected return on plan assets	(12,815)	(10,317)		(38,444)	(30,950)
Prior service cost amortization	339	218		1,015	654
Net actuarial loss amortization	3,202	2,325		9,606	6,975
Pension plan cost	9,084	$ 8,572		$ 27,252	$ 25,715
Erie Insurance Exchange (EIE)
Postretirement Benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)				59.00%
Employee pension plan | Qualified plan | Funded plan
Postretirement Benefits
Employer contribution			$ 80,000
Employee pension plan | Qualified plan | Funded plan | Erie Family Life Insurance Company (EFL)
Postretirement Benefits
Contingent liability for amount of nonparticipating annuity contracts the employee pension plan purchased from EFL	$ 18,100			$ 18,100