Deferred Policy Acquisition Costs (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in insurance subsidiaries' deferred policy acquisition costs
Balance, January 1	$ 36,424,955	$ 34,445,579	$ 32,844,179
Acquisition costs deferred	78,010,742	70,550,376	67,955,400
Amortization charged to earnings	(74,314,000)	(68,571,000)	(66,354,000)
Balance, December 31	$ 40,121,697	$ 36,424,955	$ 34,445,579