Investments - Summary of Financial Information (Detail) - Donegal Financial Services Corporation [Member] - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Balance sheets:
Total assets	$ 541,225,000		$ 535,590,000
Total liabilities	462,113,000		457,101,000
Stockholders' equity	79,112,000		78,489,000
Total liabilities and stockholders' equity	541,225,000		$ 535,590,000
Income statements:
Net income	$ 483,000	$ 73,000