Comprehensive Income (AOCI Rollforward) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018	Dec. 31, 2018	[1]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,904,334,235	$ 1,921,499,312	$ 1,861,751,660	[1]	$ 2,049,518,261
Comprehensive Income	110,636,126	109,692,931	325,974,721		328,935,897
Balance at end of period	1,921,328,263	1,843,104,255	1,921,328,263		1,843,104,255
Accumulated other comprehensive loss, end of period	(762,505)		(762,505)			$ (1,600,338)
Accumulated  Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	499,221	(479,104)	(1,600,338)		7,193,383
Balance at end of period	(762,505)	(2,121,990)	(762,505)		(2,121,990)
Accumulated other comprehensive loss, end of period	(762,505)	(2,121,990)	(762,505)		(2,121,990)
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(1,851,574)	(194,395)	(1,674,887)		645,030
Other Comprehensive income (loss) before reclassifications	(1,623,102)	(1,174,213)	(1,799,789)		(2,013,638)
Comprehensive Income	(1,623,102)	(1,174,213)	(1,799,789)		(2,013,638)
Balance at end of period	(3,474,676)	(1,368,608)	(3,474,676)		(1,368,608)
Unrealized gains (losses) on available-for-sale debt securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	2,350,795	(271,939)	74,549		(16,349)
Other Comprehensive income (loss) before reclassifications	657,128	(276,010)	3,106,369		33,941
Amounts reclassified from accumulated other comprehensive income	(295,752)	(205,433)	(468,747)		(770,974)
Comprehensive Income	361,376	(481,443)	2,637,622		(737,033)
Balance at end of period	2,712,171	(753,382)	2,712,171		(753,382)
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	0	(12,770)	0		(78,026)
Other Comprehensive income (loss) before reclassifications	0	114,889	0		175,308
Amounts reclassified from accumulated other comprehensive income	0	(102,119)	0		(97,282)
Comprehensive Income	0	12,770	0		78,026
Balance at end of period	$ 0	$ 0	$ 0		$ 0

[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.