Consolidated Statement of Comprehensive Income (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Comprehensive Income [Abstract]
Net Income	$ 222,929,949	$ 168,586,840	$ 164,668,228
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	48,989	328,976	1,563,054
Unrealized gains (losses) on available-for sales securities, net	6,701,020	7,230,048	(17,442,698)
Other comprehensive income (loss), before tax	6,750,009	7,559,024	(15,879,644)
Provision for income taxes related to components of other comprehensive income	2,345,357	2,530,516	(6,104,944)
Other comprehensive Income (loss), net of tax	4,404,652	5,028,508	(9,774,700)
Comprehensive Income	$ 227,334,601	$ 173,615,348	$ 154,893,528