Unaudited Condensed Consolidated Statements of Comprehensive Income - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 109,023,982	$ 88,535,947	$ 220,272,725	$ 186,092,688
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	(2,465,603)	1,495,210	(839,425)	1,683,800
Unrealized gains on derivatives	15,556	494,885	82,604	1,136,860
Unrealized gains (losses) on debt securities, net	(302,252)	952,365	(323,532)	3,122,619
Other comprehensive income, before tax	(2,752,299)	2,942,460	(1,080,353)	5,943,279
Expense (Benefit) for income taxes related to components of other comprehensive income	(60,206)	506,538	(50,594)	1,490,818
Other comprehensive income, net of tax	(2,692,093)	2,435,922	(1,029,759)	4,452,461
Comprehensive Income	$ 106,331,889	$ 90,971,869	$ 219,242,966	$ 190,545,149