Significant Accounting Policies - Recently Adopted Accounting Standards (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2020 USD ($) obligation	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Agent loans, allowance for credit loss		$ 1,100
Cumulative effect adjustment		1,188,048	$ 1,133,253	$ 973,672					$ 857,344
Available-for-sales securities, allowance for credit loss		$ 200			$ 600
Performance obligations under subscriber's agreement | obligation		2
Management fee rate as a percent of direct and affiliated assumed written premiums of the exchange		25.00%
Deferred tax asset		$ 12,341	17,186
Cumulative effect adjustment due to ASC 606		$ 2,393,624	$ 2,377,558
Erie Insurance Exchange (EIE)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Management fee rate as a percent of direct and affiliated assumed written premiums of the exchange		25.00%	25.00%	25.00%
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment	[1]		$ (1,075)						$ (38,392)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets							$ 32,700
Operating lease liability							$ 32,100
Accounting Standards Update 2014-09 | Adjustments due to ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract liability								$ 48,500
Deferred tax asset								10,200
Cumulative effect adjustment due to ASC 606								$ (38,300)
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Agent loans, allowance for credit loss						$ 800
Cumulative effect adjustment			$ 1,100
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment | Erie Insurance Exchange (EIE)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Receivables from Erie Insurance Exchange, allowance for credit loss						$ 600

[1] (1) Cumulative effect adjustments in 2018 are primarily related to the implementation of new revenue recognition guidance effective January 1, 2018. The Cumulative effect adjustment in 2020 is related to the implementation of new credit loss allowance accounting guidance effective January 1, 2020. See Note 2, "Significant Accounting Policies."