Investments - Summary of Financial Information (Detail) (Donegal Financial Services Corporation [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Donegal Financial Services Corporation [Member]
Balance sheets:
Total assets	$ 514,654		$ 514,654		$ 509,670
Total liabilities	440,762		440,762		433,490
Stockholders' equity	73,892		73,892		76,180
Total liabilities and stockholders' equity	514,654		514,654		509,670
Income statements:
Net income	$ 1,401	$ 2,303	$ 3,659	$ 4,739