Comprehensive Income (AOCI Rollforward) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021		Mar. 31, 2020	Dec. 31, 2020	[1]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,963,943,128	[1]	$ 1,938,087,820
Comprehensive income	108,554,485		91,009,698
Balance at end of period	1,960,980,714		1,834,605,633
Accumulated other comprehensive income (loss), end of period	1,954,667			$ 6,851,052
Accumulated  Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	6,851,052		(1,289,103)
Balance at end of period	1,954,667		214,794
Accumulated other comprehensive income (loss), end of period	1,954,667		214,794
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	769,045		(2,384,589)
Other Comprehensive income (loss) before reclassifications	(852,412)		(692,090)
Comprehensive income	(852,412)		(692,090)
Balance at end of period	(83,367)		(3,076,679)
Unrealized gains (losses) on available-for-sale debt securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	6,082,007		1,095,486
Other Comprehensive income (loss) before reclassifications	(3,692,619)		2,225,196
Comprehensive income	(4,043,973)		2,195,987
Amounts reclassified from accumulated other comprehensive income	(351,354)		(29,209)
Balance at end of period	$ 2,038,034		$ 3,291,473

[1] The condensed consolidated balance sheet at December 31, 2020 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.