Transactions with Affiliates - Schedule of Insurance Subsidiaries Ceded to Donegal Mutual Pursuant to these 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
Insurance Subsidiaries [Member]
Ceded Credit Risk [Line Items]
Premiums earned	275,126,732	274,932,234	260,545,919
Catastrophe Reinsurance [Member] | Insurance Subsidiaries [Member]
Ceded Credit Risk [Line Items]
Premiums earned	14,404,636	19,190,067	17,215,273
Losses and loss expenses	13,769,736	12,899,927	8,953,411
Liability for losses and loss expenses	$ 3,149,907	$ 4,847,176	$ 3,399,207