Transactions with Affiliates - Schedule of Reinsurance Ceded to Donegal Mutual Pursuant to these Quota-Share Reinsurance Agreements (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Ceded Credit Risk [Line Items]
Premiums earned	$ 314,859,014	$ 326,198,234	$ 310,179,267
Prepaid reinsurance premiums	142,475,767	135,379,777
Donegal Mutual [Member]
Ceded Credit Risk [Line Items]
Premiums earned	42,079,112	42,813,929	42,578,047
Losses and loss expenses	19,617,787	23,175,456	24,978,631
Prepaid reinsurance premiums	19,217,849	19,047,084	19,827,115
Liability for losses and loss expenses	$ 36,597,834	$ 38,434,078	$ 36,396,109