Unaudited Condensed Consolidated Statements of Comprehensive Income - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 90,230,335	$ 92,064,646	$ 276,323,023	$ 258,829,882
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	1,182,152	162,343	2,865,952	(1,266,636)
Unrealized gains (losses) on derivatives	239,215	1,070,229	1,376,077	(401,803)
Unrealized gains on available-for sales securities, net	2,287,103	3,345,885	5,409,722	3,409,021
Other comprehensive income (loss), before tax	3,708,470	4,578,457	9,651,751	1,740,582
Expense (Benefit) for income taxes related to components of other comprehensive income (loss)	884,211	1,545,640	2,375,031	1,052,527
Other comprehensive income (loss), net of tax	2,824,259	3,032,817	7,276,720	688,055
Comprehensive Income	$ 93,054,594	$ 95,097,463	$ 283,599,743	$ 259,517,937