Investments - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amount of securities with fair value	$ 275,804,907		$ 241,879,775
Proceeds from sales of available for sale debt securities	24,989,844	44,771,114
Available for sale debt securities were sold and called for realized gains	$ 254,841	$ 964,175
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities issued contained unrealized Loss	7
Securities issued	10
U.S. Government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities issued contained unrealized Loss	24
Securities issued	33
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities issued contained unrealized Loss	8
Securities issued	10
States and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities issued contained unrealized Loss	29
Securities issued	147