Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 68,566,071	$ 45,430,567
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	(91,250)	(601,749)
Unrealized gains on available-for sales securities, net	(3,692,791)	9,194,861
Other comprehensive income, before tax	(3,784,041)	8,593,112
Provision for income taxes related to components of other comprehensive income	(1,292,477)	3,218,201
Other comprehensive income, net of tax	(2,491,564)	5,374,911
Comprehensive Income	$ 66,074,507	$ 50,805,478