Reinsurance - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Ceded Credit Risk [Line Items]
Percentage of share in results of pooled business subsidiary	80.00%
Percentage of share in results of pooled business owned by third party	20.00%
Excess of loss reinsured under an agreement	$ 1.0
Percentage of accumulation of losses	100.00%
Natural disasters, over a set retention	5.0
Natural disasters, aggregate annual deduction	1.5
Quota share reinsurance percentage	20.00%
Donegal Mutual [Member]
Ceded Credit Risk [Line Items]
Maximum amount of loss coverage under reinsurance agreement of property catastrophe	$ 145.0