v3.10.0.1

Organization - Additional Information (Detail)		3 Months Ended		9 Months Ended	62 Months Ended
	Jun. 11, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($) Segment	Sep. 30, 2018 USD ($) shares	Jul. 18, 2013 shares
Business Acquisition [Line Items]
Operations commenced date				Aug. 26, 1986
Stock ownership percentage owned by third party				51.80%
Number of operating segments | Segment				4
Voting power percentage of outstanding common stock				72.00%
Restructuring charge for employee termination costs				$ 1,900,000
Restructuring charges paid for employee termination costs				835,000
Accrual of restructuring charge				$ 1,100,000
Atlantic States [Member]
Business Acquisition [Line Items]
Percentage of share in results of pooled business subsidiary				80.00%
Donegal Mutual [Member]
Business Acquisition [Line Items]
Percentage of share in results of pooled business owned by third party				20.00%
DFSC and North West [Member] | Donegal Mutual Insurance Company [Member]
Business Acquisition [Line Items]
Consideration from sale of business	$ 85,000,000
Proceeds from dividend	$ 30,000,000
Peninsula [Member]
Business Acquisition [Line Items]
Impairment charge related to real estate transaction			$ 1,000,000
Fair value of real asset held for sale			$ 1,200,000	$ 1,200,000	$ 1,200,000
Peninsula [Member] | Scenario, Forecast [Member]
Business Acquisition [Line Items]
Expected proceeds from sale of real estate		$ 1,200,000
Donegal Financial Services Corporation [Member]
Business Acquisition [Line Items]
Outstanding stock ownership percentage			48.20%	48.20%	48.20%
Donegal Financial Services Corporation [Member] | DFSC and North West [Member]
Business Acquisition [Line Items]
Outstanding stock ownership percentage	48.20%
Dividend payment to be received	$ 14,500,000
Donegal Financial Services Corporation [Member] | DFSC and North West [Member] | Minimum [Member]
Business Acquisition [Line Items]
Consideration from sale of business and dividend	38,900,000
Donegal Financial Services Corporation [Member] | DFSC and North West [Member] | Maximum [Member]
Business Acquisition [Line Items]
Consideration from sale of business and dividend	$ 43,000,000
Class A Common Stock [Member]
Business Acquisition [Line Items]
Stock ownership percentage held by major shareholder				43.00%
Class A Common Stock [Member] | Stock Repurchase Program Two [Member]
Business Acquisition [Line Items]
Authority to purchase shares | shares						500,000
Common stock shares purchased | shares					57,658
Class B Common Stock [Member]
Business Acquisition [Line Items]
Stock ownership percentage held by major shareholder				84.00%

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