Unaudited Condensed Consolidated Statements of Comprehensive Income - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 92,064,646	$ 78,332,425	$ 258,829,882	$ 230,074,303
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	162,343	(396,686)	(1,266,636)	(1,038,892)
Unrealized gains (losses) on derivatives	1,070,229	(1,275,655)	(401,803)	(3,143,576)
Unrealized gains (losses) on available-for sales securities, net	3,345,885	(11,808,718)	3,409,021	(15,372,962)
Other comprehensive income (loss), before tax	4,578,457	(13,481,059)	1,740,582	(19,555,430)
Expense (Benefit) for income taxes related to components of other comprehensive income (loss)	1,545,640	(4,579,531)	1,052,527	(6,480,789)
Other comprehensive income (loss), net of tax	3,032,817	(8,901,528)	688,055	(13,074,641)
Comprehensive Income	$ 95,097,463	$ 69,430,897	$ 259,517,937	$ 216,999,662