Transactions with Affiliates - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Ceded Credit Risk [Line Items]
Premiums and losses related to certain products	63.90%	64.30%	64.50%
Excess of loss reinsured under an agreement	$ 1,000,000
Charges for services	126,153,511	$ 124,999,770	$ 122,428,117
Accounts with UCB	50,252,479	32,373,544
Interest on UCB accounts	$ 538,311	286,410	87,941
Minimum [Member] | Lease Office Equipment And Automobile [Member]
Ceded Credit Risk [Line Items]
Lease office equipment and automobiles range	3 years
Maximum [Member] | Lease Office Equipment And Automobile [Member]
Ceded Credit Risk [Line Items]
Lease office equipment and automobiles range	10 years
Atlantic States [Member]
Ceded Credit Risk [Line Items]
Percentage of share in results of pooled business subsidiary	80.00%
Coverage under catastrophic occurrence	$ 2,500,000	2,000,000	2,000,000
Donegal Mutual [Member]
Ceded Credit Risk [Line Items]
Percentage of share in results of pooled business owned by third party	20.00%
Premiums and losses related to certain products	100.00%
Premiums and losses related to business of MICO	25.00%
Excess of loss reinsured under an agreement	$ 500,000
Period of Donegal Mutual under lease agreement	10 years
Le Mars [Member]
Ceded Credit Risk [Line Items]
Premiums and losses related to certain products	100.00%
Coverage under catastrophic occurrence	$ 1,000,000	750,000	750,000
Southern [Member]
Ceded Credit Risk [Line Items]
Premiums and losses related to certain products	100.00%
Coverage under catastrophic occurrence	$ 2,000,000	$ 1,500,000	$ 1,500,000
Excess of loss reinsured under an agreement	500,000
Insurance Subsidiaries [Member]
Ceded Credit Risk [Line Items]
Coverage under catastrophic occurrence	5,000,000
Excess of loss reinsured under an agreement	$ 5,000,000