Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated other comprehensive income (loss), before tax
Amortization of prior service costs		$ (871)	$ (696)
Amortization of net actuarial loss		(9,301)	(8,111)
Settlement loss		(302)
OCI (loss)		(10,300)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of year	$ (156,059)	(121,381)
OCI (loss)		(190)	43	$ (4,280)
OCI (loss)		8,105	24,560	(25,117)
Reclassification adjustment		0
OCI (loss)		(8,295)	(24,517)	20,837
AOCI (loss), end of year		$ (156,059)	(121,381)
Federal statutory income tax rate
Corporate tax rate		35.00%
Investment securities:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of year	3,410	$ 3,954	3,888	10,473
OCI (loss) before reclassifications - pre TCJA		(648)	(385)	(7,651)
OCI before reclassifications - post TCJA		1,162
Realized investment (gains) losses		(1,240)	35	(492)
Impairment losses		182	416	1,558
OCI (loss)		(544)	66	(6,585)
AOCI (loss), end of year		3,410	3,954	3,888
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of year	716	1,384	1,361	3,666
OCI (loss) before reclassifications - pre TCJA		(227)	(135)	(2,678)
OCI before reclassifications - post TCJA		243
Realized investment (gains) losses		(434)	12	(172)
Impairment losses		64	146	545
OCI (loss)		(354)	23	(2,305)
Reclassification adjustment		(314)
AOCI (loss), end of year		716	1,384	1,361
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of year	2,694	2,570	2,527	6,807
OCI (loss) before reclassifications - pre TCJA		(421)	(250)	(4,973)
OCI before reclassifications - post TCJA		919
Realized investment (gains) losses		(806)	23	(320)
Impairment losses		118	270	1,013
OCI (loss)		(190)	43	(4,280)
Reclassification adjustment		314
AOCI (loss), end of year		2,694	2,570	2,527
Pension and other postretirement plans:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of year	(200,954)	(190,695)	(152,910)	(191,552)
OCI (loss) before reclassifications		(20,314)	(46,244)	24,094
Amortization of prior service costs		871	695	668
Amortization of net actuarial loss		8,882	7,764	13,880
Settlement loss		302
OCI (loss)		(10,259)	(37,785)	38,642
AOCI (loss), end of year		(200,954)	(190,695)	(152,910)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of year	(42,201)	(66,744)	(53,519)	(67,044)
OCI (loss) before reclassifications		(7,111)	(16,185)	8,433
Amortization of prior service costs		306	243	234
Amortization of net actuarial loss		3,109	2,717	4,858
Settlement loss		106
Impact of change in tax rate		1,436
OCI (loss)		(2,154)	(13,225)	13,525
Reclassification adjustment		26,697
AOCI (loss), end of year		(42,201)	(66,744)	(53,519)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of year	(158,753)	(123,951)	(99,391)	(124,508)
OCI (loss) before reclassifications		(13,203)	(30,059)	15,661
Amortization of prior service costs		565	452	434
Amortization of net actuarial loss		5,773	5,047	9,022
Settlement loss		196
Impact of change in tax rate		(1,436)
OCI (loss)		(8,105)	(24,560)	25,117
Reclassification adjustment		(26,697)
AOCI (loss), end of year		(158,753)	(123,951)	(99,391)
Total
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of year	(197,544)	(186,741)	(149,022)	(181,079)
OCI (loss)		(544)	66	(6,585)
OCI (loss)		(10,259)	(37,785)	38,642
OCI (loss)		(10,803)	(37,719)	32,057
AOCI (loss), end of year		(197,544)	(186,741)	(149,022)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of year	(41,485)	(65,360)	(52,158)	(63,378)
OCI (loss)		(354)	23	(2,305)
OCI (loss)		(2,154)	(13,225)	13,525
Reclassification adjustment		26,383
OCI (loss)		(2,508)	(13,202)	11,220
AOCI (loss), end of year		(41,485)	(65,360)	(52,158)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of year	$ (156,059)	(121,381)	(96,864)	(117,701)
OCI (loss)		(190)	43	(4,280)
OCI (loss)		(8,105)	(24,560)	25,117
Reclassification adjustment		(26,383)
OCI (loss)		(8,295)	(24,517)	20,837
AOCI (loss), end of year		$ (156,059)	$ (121,381)	$ (96,864)
Tax Cuts and Jobs Act of 2017 \| Scenario, Forecast
Federal statutory income tax rate
Corporate tax rate	21.00%

AOCI Attributable to Parent, Tax [Abstract]

No definition available.

Name:	erie_AOCIAttributabletoParentTaxAbstract
Namespace Prefix:	erie_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income for defined benefit plan, attributable to parent, remeasured pursuant to the Tax Cuts and Jobs Act of 2017.

+ References

No definition available.

+ Details

Name:	erie_TaxCutsandJobsActof2017OtherComprehensiveIncomeLossDefinedBenefitPlanafterReclassificationAdjustmentTaxAttributabletoParent
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan, attributable to parent, remeasured pursuant to the Tax Cuts and Jobs Act of 2017.

+ References

No definition available.

+ Details

Name:	erie_TaxCutsandJobsActof2017OtherComprehensiveIncomeLossDefinedBenefitPlanafterTaxandReclassificationAdjustmentAttributabletoParent
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities remeasured pursuant to the Tax Cuts and Jobs Act of 2017.

+ References

No definition available.

+ Details

Name:	erie_TaxCutsandJobsActof2017OtherComprehensiveIncomeLossUnrealizedHoldingGainLossonSecuritiesArisingDuringPeriodNetofTax
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities remeasured pursuant to the Tax Cuts and Jobs Act of 2017.

+ References

No definition available.

+ Details

Name:	erie_TaxCutsandJobsActof2017OtherComprehensiveIncomeLossUnrealizedHoldingGainLossonSecuritiesArisingDuringPeriodTax
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities remeasured pursuant to the Tax Cuts and Jobs Act of 2017.

+ References

No definition available.

+ Details

Name:	erie_TaxCutsandJobsActof2017OtherComprehensiveIncomeLossUnrealizedHoldingGainLossonSecuritiesArisingDuringPeriodbeforeTax
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, net of tax, of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from remeasurement of deferred tax pursuant to Tax Cuts and Jobs Act of 2017.

+ References

No definition available.

+ Details

Name:	erie_TaxCutsandJobsActof2017ReclassificationfromAOCItoRetainedEarningsNetofTax
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of tax of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from remeasurement of deferred tax pursuant to Tax Cuts and Jobs Act of 2017.

+ References

No definition available.

+ Details

Name:	erie_TaxCutsandJobsActof2017ReclassificationfromAOCItoRetainedEarningsTax
Namespace Prefix:	erie_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

+ Details

Name:	us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of increase (decrease) in accumulated equity from transactions and other events and circumstances from non-owner sources, attributable to parent. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners).

+ References

No definition available.

+ Details

Name:	us-gaap_AociBeforeTaxAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of tax expense (benefit) allocated to accumulated other comprehensive income (loss) attributable to parent.

+ References

No definition available.

+ Details

Name:	us-gaap_AociTaxAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before tax, after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities, attributable to parent entity. Excludes amounts related to other than temporary impairment (OTTI) loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569643-111683

+ Details

Name:	us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentBeforeTaxPortionAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities, attributable to parent entity. Excludes amounts related to other than temporary impairment (OTTI) loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569643-111683

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683

+ Details

Name:	us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive (income) loss for defined benefit plan, attributable to parent entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569643-111683

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684

+ Details

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

- Definition

Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan, attributable to parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i-k)
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

+ Details

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

- Definition

Amount, after reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income for defined benefit plan, attributable to parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569643-111683

+ Details

Name:	us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansTaxPortionAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of tax expense (benefit) for increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan.

+ References

+ Details

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

- Definition

Amount, before tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e689-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e689-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

+ References

+ Details

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

- Definition

Amount of tax expense (benefit), after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e640-108580

+ Details

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

- Definition

Amount before tax of other comprehensive income (loss) attributable to parent entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569643-111683

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, before tax, of increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e689-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after tax, of increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e689-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount after tax of other comprehensive income (loss) attributable to parent entity.

+ References

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, before tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

+ Details

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

- Definition

Amount, after tax, before reclassification adjustment, of (increase) decrease in accumulated other comprehensive income of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

+ Details

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

- Definition

Amount, before reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income for defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e640-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i-k)
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansBeforeReclassificationAdjustmentsTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount before tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e689-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

+ Details

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

- Definition

Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e689-108580

+ Details

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

- Definition

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

+ References

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount before tax of reclassification adjustment from accumulated other comprehensive income for unrealized loss realized upon the write-down of available-for-sale securities.

+ References

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForWritedownOfSecuritiesBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized loss realized upon the write-down of available-for-sale securities.

+ References

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForWritedownOfSecuritiesNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive income for unrealized loss realized upon the write-down of available-for-sale securities.

+ References

+ Details

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

- Definition

Amount, before tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e689-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

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

- Definition

Amount, after tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e689-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

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

- Definition

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

+ References

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.

+ References

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

+ References

+ Details

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

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherComprehensiveIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	erie_TaxCutsandJobsActof2017Axis=erie_TaxCutsandJobsActof2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: