Comprehensive Income (AOCI Rollforward) (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	[1]			$ 2,049,518,261
Comprehensive Income		$ 106,331,889	$ 90,971,869	219,242,966	$ 190,545,149
Balance at end of period		1,921,499,312		1,921,499,312
Accumulated other comprehensive income (loss), end of period
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at end of period		(479,104)	3,181,156	(479,104)	3,181,156
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		2,271,208	(2,674,409)	645,030	(2,862,999)
Other Comprehensive (loss) income before reclassifications		(2,465,603)	1,495,210	(839,425)	1,683,800
Comprehensive Income		(2,465,603)	1,495,210	(839,425)	1,683,800
Balance at end of period		(194,395)	(1,179,199)	(194,395)	(1,179,199)
Unrealized gains (losses) on available-for-sale debt securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(33,160)	4,199,640	(16,349)	2,788,975
Other Comprehensive (loss) income before reclassifications		(238,555)	1,164,243	309,951	2,739,626
Amounts reclassified from accumulated other comprehensive income		(224)	(545,206)	(565,541)	(709,924)
Comprehensive Income		(238,779)	619,037	(255,590)	2,029,702
Balance at end of period		(271,939)	4,818,677	(271,939)	4,818,677
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(25,059)	(779,997)	(78,026)	(1,197,281)
Other Comprehensive (loss) income before reclassifications		17,246	(23,617)	60,419	123,701
Amounts reclassified from accumulated other comprehensive income		(4,957)	345,292	4,837	615,258
Comprehensive Income		12,289	321,675	65,256	738,959
Balance at end of period		$ (12,770)	$ (458,322)	$ (12,770)	$ (458,322)

[1] The condensed consolidated balance sheet at December 31, 2017 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements.3