Investments - Summary of Financial Information (Detail) - Donegal Financial Services Corporation [Member] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Balance sheets:
Total assets	$ 544,943,000		$ 544,943,000		$ 535,590,000
Total liabilities	464,454,000		464,454,000		457,101,000
Stockholders' equity	80,489,000		80,489,000		78,489,000
Total liabilities and stockholders' equity	544,943,000		544,943,000		$ 535,590,000
Income statements:
Net income	$ 802,000	$ 634,000	$ 1,285,000	$ 707,000