Unaudited Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 76,726,746	$ 52,097,397	$ 145,292,817	$ 97,527,964
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	(241,489)	229,115	(332,739)	(372,634)
Unrealized gains (losses) on available-for sales securities, net	(2,653,194)	(3,674,340)	(6,345,985)	5,520,521
Other comprehensive income (loss), before tax	(2,894,683)	(3,445,225)	(6,678,724)	5,147,887
Provision (Benefit) for income taxes related to components of other comprehensive income	(928,618)	(1,286,019)	(2,221,095)	1,932,182
Other comprehensive income, net of tax	(1,966,065)	(2,159,206)	(4,457,629)	3,215,705
Comprehensive Income	$ 74,760,681	$ 49,938,191	$ 140,835,188	$ 100,743,669