Consolidated Statements of Comprehensive (Loss) Income (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 7,653,734	$ 6,839,384	$ 16,758,157	$ 16,872,598
Unrealized (loss) gain on securities:
Unrealized holding (loss) income during the period, net of income tax (benefit) expense	(1,175,052)	6,527,358	(25,511,627)	11,096,463
Reclassification adjustment for gains included in net income, net of income tax	(230,449)	(866,010)	(1,942,849)	(3,399,297)
Other comprehensive (loss) income	(1,405,501)	5,661,348	(27,454,476)	7,697,166
Comprehensive (loss) income	$ 6,248,233	$ 12,500,732	$ (10,696,319)	$ 24,569,764