Comprehensive Income (AOCI Rollforward) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020	Dec. 31, 2020	[1]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,916,318,989	$ 1,822,607,413	$ 1,963,943,128	[1]	$ 1,938,087,820
Net current-period change	(994,438)	1,707,816	(3,580,452)		5,736,163
Balance at end of period	1,887,630,286	1,895,612,299	1,887,630,286		1,895,612,299
Accumulated other comprehensive income, end of period	3,270,600		3,270,600			$ 6,851,052
Accumulated  Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	4,265,038	2,739,244	6,851,052		(1,289,103)
Net current-period change	(994,438)	1,707,816	(3,580,452)		5,736,163
Balance at end of period	3,270,600	4,447,060	3,270,600		4,447,060
Accumulated other comprehensive income, end of period	3,270,600	4,447,060	3,270,600		4,447,060
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	879,832	(2,940,052)	769,045		(2,384,589)
Other Comprehensive income (loss) before reclassifications	(349,165)	1,823,667	(238,378)		1,268,204
Net current-period change	(349,165)	1,823,667	(238,378)		1,268,204
Balance at end of period	530,667	(1,116,385)	530,667		(1,116,385)
Unrealized gains (losses) on available-for-sale debt securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	3,385,206	5,679,296	6,082,007		1,095,486
Other Comprehensive income (loss) before reclassifications	(645,273)	208,503	(2,727,750)		5,543,455
Amounts reclassified from accumulated other comprehensive income	0	(324,354)	(614,324)		(1,075,496)
Net current-period change	(645,273)	(115,851)	(3,342,074)		4,467,959
Balance at end of period	$ 2,739,933	$ 5,563,445	$ 2,739,933		$ 5,563,445

[1] The condensed consolidated balance sheet at December 31, 2020 has been derived from the audited consolidated 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.