Incentive and Deferred Compensation Plans (Details) - USD ($)	1 Months Ended				2 Months Ended		12 Months Ended
	Nov. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	May. 31, 2014	Dec. 17, 2015	Jun. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class A
Incentive and deferred compensation plans
Total cost of shares purchased outside of publicly announced stock repurchase program							$ 10,400,000	$ 4,900,000
Class A | Performance shares
Incentive and deferred compensation plans
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)							111,535	64,398
Long-term incentive plan
Incentive and deferred compensation plans
Vesting period of performance and/or service condition(s) (in years and/or months)							3 years
Maximum dollar amount which may be received by any single participant during any specified period							$ 5,000,000
Compensation cost related to share-based compensation plan awards							13,407,000	$ 12,523,000	$ 7,941,000
Tax benefits recognized in income related to award expense							4,700,000	4,400,000	$ 2,800,000
Total unrecognized compensation cost related to share-based compensation plan awards pertaining to open performance periods							$ 11,100,000
Expected period of recognition related to unrecognized compensation cost (in years)							2 years
Long-term incentive plan | Class A
Incentive and deferred compensation plans
Maximum number of shares authorized for grant (in shares)							1,500,000
Maximum number of shares which may be received by any single participant during any specified period (in shares)							250,000
Average price per share for shares purchased (in dollars per share)		$ 81.91	$ 76.21			$ 76.21
Total cost of shares purchased outside of publicly announced stock repurchase program		$ 100,000				$ 4,100,000
Long-term incentive plan | Class A | Performance shares
Incentive and deferred compensation plans
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)		1,567				54,371
Long-term incentive plan | 2013-2015 performance period
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards							$ 13,500,000
Long-term incentive plan | 2012-2014 performance period
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards		$ 8,200,000
Long-term incentive plan | 2012-2014 performance period | Class A
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards		$ 100,000
Average price per share for shares delivered (in dollars per share)		$ 81.04
Long-term incentive plan | 2012-2014 performance period | Class A | Performance shares
Incentive and deferred compensation plans
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)		1,567
Long-term incentive plan | 2011-2013 performance period | Class A
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards			$ 4,100,000
Average price per share for shares delivered (in dollars per share)			$ 75.36			$ 75.36
Long-term incentive plan | 2011-2013 performance period | Class A | Performance shares
Incentive and deferred compensation plans
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)			54,371
Equity compensation plan
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards							400,000	$ 300,000
Total unrecognized compensation cost related to share-based compensation plan awards pertaining to open performance periods							$ 700,000
Expected period of recognition related to unrecognized compensation cost (in years)							3 years
Equity compensation plan | Class A
Incentive and deferred compensation plans
Maximum number of shares authorized for grant (in shares)							100,000
Maximum number of shares which may be received by any single participant during any specified period (in shares)							5,000
Restricted stock units granted							5,500	8,750	0
Stock compensation plan for outside directors
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards							$ 1,900,000	$ 2,200,000	$ 1,100,000
Stock compensation plan for outside directors | Class A
Incentive and deferred compensation plans
Average price per share for shares purchased (in dollars per share)	$ 87.03			$ 76.45	$ 94.99
Total cost of shares purchased outside of publicly announced stock repurchase program	$ 1,100,000			$ 600,000	$ 9,000,000
Stock compensation plan for outside directors | Class A | Performance shares
Incentive and deferred compensation plans
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)	12,230			7,227	94,938
Stock compensation plan for outside directors | Three month vesting period | Class A
Incentive and deferred compensation plans
Vesting period of performance and/or service condition(s) (in years and/or months)							3 months
Vesting percent of the grant in Class A common stock (as a percent)							25.00%
Erie Insurance Exchange (EIE) | Long-term incentive plan
Incentive and deferred compensation plans
Incentive plan compensation cost reimbursed to Indemnity from the Exchange (as a percent)							33.00%
Erie Insurance Exchange (EIE) | Equity compensation plan
Incentive and deferred compensation plans
Incentive plan compensation cost reimbursed to Indemnity from the Exchange (as a percent)							31.00%