Consolidated Statement of Comprehensive Income - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 347,591,276	$ 318,469,859	$ 288,604,579
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	(2,818,090)	(1,448,808)	(1,104,023)
Unrealized gains (losses) on derivatives	1,105,468	(1,471,736)	(1,475,702)
Unrealized gains (losses) on available-for-sale securities, net	3,013,951	(15,443,716)	(13,229,414)
Other comprehensive income (loss), before tax	1,301,328	(18,364,260)	(15,809,139)
Expense (Benefit) for income taxes related to components of other comprehensive income (loss)	1,441,798	(5,920,409)	(5,146,791)
Other comprehensive (loss), net of tax	(140,469)	(12,443,851)	(10,662,348)
Comprehensive Income	$ 347,450,807	$ 306,026,008	$ 277,942,231