Investments - Impairments on Available-For-Sale Securities and Agent Loans (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Available-for-sale securities:
Intent to sell	$ 0	$ 0	$ 0	$ (2,242)
Credit (impaired) recovered	(1)	(17)	86	(658)
Total available-for-sale securities	(1)	(17)	86	(2,900)
Agent loans - expected credit losses	0	0	0	(170)
Net impairment (losses) recoveries recognized in earnings	$ (1)	$ (17)	$ 86	$ (3,070)

Available-For-Sale Debt Securities And Financing Receivables, Impairment Loss (Recovery) Recognized in Earnings

No definition available.

Name:	erie_AvailableForSaleDebtSecuritiesAndFinancingReceivablesImpairmentLossRecoveryNet
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Available-For-Sale Debt Securities, Impairment Loss Recognized in Earnings

+ References

No definition available.

+ Details

Name:	erie_AvailableForSaleDebtSecuritiesImpairmentLossRecovery
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of impairment recognized in earnings on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) from intent to sell or more likely than not will be required to sell before recovery of amortized cost basis.

+ References

No definition available.

+ Details

Name:	erie_DebtSecuritiesAvailableforsaleSellbeforeRecovery
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of expense (reversal of expense) for expected credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), from change in present value of expected cash flows.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82922868-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922897-210455

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleChangeInPresentValueExpenseReversal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(11))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

Name:	us-gaap_ProvisionForLoanLossesExpensed
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration