Investments - Summary of Financial Information (Detail) - Donegal Financial Services Corporation [Member] - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Balance sheets:
Total assets	$ 553,190,379	$ 567,935,408
Total liabilities	468,187,592	487,603,999
Stockholders' equity	85,002,787	80,331,409
Total liabilities and stockholders' equity	553,190,379	567,935,408
Income statements:
Net income	$ 5,457,636	$ 3,362,861	$ 2,252,456