Comprehensive Income (AOCI Rollforward) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019		Mar. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 1,861,751,660	[1]	$ 2,049,518,261
Comprehensive Income	105,605,015		112,911,077
Ending balance	1,857,074,747		1,969,977,496
Accumulated  Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,600,338)		7,193,383
Ending balance	(275,734)		2,212,989
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,674,887)		645,030
Other Comprehensive income (loss) before reclassifications	298,999		1,626,178
Comprehensive Income	298,999		1,626,178
Ending balance	(1,375,888)		2,271,208
Unrealized gains (losses) on available-for-sale debt securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	74,549		(16,349)
Other Comprehensive income (loss) before reclassifications	1,095,581		548,506
Amounts reclassified from accumulated other comprehensive income	(69,976)		(565,317)
Comprehensive Income	1,025,605		(16,811)
Ending balance	1,100,154		(33,160)
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0		(78,026)
Other Comprehensive income (loss) before reclassifications	0		43,173
Amounts reclassified from accumulated other comprehensive income	0		9,794
Comprehensive Income	0		52,967
Ending balance	$ 0		$ (25,059)

[1] The condensed consolidated balance sheet at December 31, 2018 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.