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Represents the period over which performance is measured for the estimation of agent bonuses.

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Represents the maximum maturity period at date of purchase for an available-for-sale security to be considered a current asset.

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Represents the maximum maturity period at date of purchase for an investment to be considered a cash equivalent.

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No definition available.

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Represents the management fee rate, determined by the board of directors of the entity, calculated as a percentage of the direct and affiliated assumed written premiums.

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No definition available.

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Represents the quantification of the effect of adopting the new accounting standard.

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Property Plant And Equipment and Finite-Lived Intangible Assets, Net By Type [Abstract]

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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.

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements
Decrease in accumulated other comprehensive income and increase in retained earnings due to ASU 2018-02		$ 0
Cash and cash equivalents
Cash and cash equivalents, maximum maturity at the date of purchase (in months)		3 months
Available-for-sale securities
Available-for-sale securities, maximum maturity to be classified as current assets (in months)		12 months
Federal statutory income tax rate
Corporate tax rate		35.00%
Agent bonus estimates
Performance period for agent bonuses (in months)		36 months
Period of prior year actual underwriting data used to estimate agent bonuses (in years)		2 years
Erie Insurance Exchange (EIE)
Management fee rate
Indemnity's management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)		25.00%	25.00%	25.00%
Maximum \| Erie Insurance Exchange (EIE)
Management fee rate
Indemnity's management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)		25.00%
Software \| Minimum
Fixed assets
Estimated useful life (in years)		3 years
Software \| Maximum
Fixed assets
Estimated useful life (in years)		7 years
Equipment \| Minimum
Fixed assets
Estimated useful life (in years)		3 years
Equipment \| Maximum
Fixed assets
Estimated useful life (in years)		10 years
Buildings and building improvements \| Minimum
Fixed assets
Estimated useful life (in years)		20 years
Buildings and building improvements \| Maximum
Fixed assets
Estimated useful life (in years)		45 years
Scenario, Forecast \| Erie Insurance Exchange (EIE)
Management fee rate
Indemnity's management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)	25.00%
Less than 10%
Limited partnerships
Limited partnerships, general ownership percentage (as a percent)		10.00%
Nonredeemable preferred stock
New Accounting Pronouncements
Equity securities fair value		$ 12,752
Accounting Standards Update 2017-07
New Accounting Pronouncements
Other components of net benefit costs reclassified from operating expenses due to ASU 2017-07		1,900
Accounting Standards Update 2016-01 \| Nonredeemable preferred stock
New Accounting Pronouncements
Equity securities fair value		12,800
Accounting Standards Update 2016-01 \| Nonredeemable preferred stock \| Scenario, Forecast
New Accounting Pronouncements
Cumulative effect adjustment due to ASU 2016-01	$ 100
Tax Cuts and Jobs Act of 2017 \| Scenario, Forecast
Federal statutory income tax rate
Corporate tax rate	21.00%
Tax Cuts and Jobs Act of 2017 \| Accounting Standards Update 2018-02
New Accounting Pronouncements
Decrease in accumulated other comprehensive income and increase in retained earnings due to ASU 2018-02		$ (26,400)