Significant Accounting Policies (Details) - USD ($)		9 Months Ended	12 Months Ended
		Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting standards update			us-gaap:AccountingStandardsUpdate201613Member
Agent loans, allowance for credit loss		$ 1,000,000.0
Cumulative effect adjustment		1,247,217,000	$ 1,133,253,000	$ 1,194,139,000	$ 1,116,992,000		$ 1,119,271,000	$ 1,063,454,000	$ 1,013,804,000	$ 973,672,000
Available-for-sale securities, allowance for credit loss		400,000			$ 600,000
Loan Purchase Commitments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Participation amount in loan program		900,000
Loan program, guaranteed amount		$ 700,000
Loan Purchase Commitments | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum funding percentage of each loan		30.00%
Third-Party Bank | Loan Purchase Commitments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Amount of loan participation program		$ 3,100,000
Third-Party Bank | Loan Purchase Commitments | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Amount of loan participation program		$ 100,000,000
Cumulative effect adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment	[1]		(1,075,000)
Cumulative effect adjustment | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Agent loans, allowance for credit loss						$ 800,000
Cumulative effect adjustment			$ 1,100,000
Erie Insurance Exchange | Cumulative effect adjustment | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Receivables from Erie Insurance Exchange, allowance for credit loss						$ 600,000

[1] The cumulative effect adjustment is related to the implementation of new credit loss allowance accounting guidance effective January 1, 2020. See Note 2. "Significant Accounting Policies".