Comprehensive Income (AOCI Rollforward) (Details) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	[1]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	[1]			$ 1,910,424,234
Comprehensive Income		$ 93,054,594	$ 95,097,463	283,599,743	$ 259,517,937
Balance at end of period		2,026,265,199		2,026,265,199
Accumulated other comprehensive income (loss), end of period		6,005,415	(442,780)	6,005,415	(442,780)	$ (1,271,305)
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(1,179,199)	(1,473,888)	(2,862,999)	(44,909)
Other Comprehensive income (loss) before reclassifications		1,182,152	162,343	2,865,952	(1,266,636)
Comprehensive Income		1,182,152	162,343	2,865,952	(1,266,636)
Balance at end of period		2,953	(1,311,545)	2,953	(1,311,545)
Unrealized gains on available-for-sale securities:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		4,818,677	870,945	2,788,975	829,907
Other Comprehensive income (loss) before reclassifications		1,371,712	2,269,315	4,111,338	1,993,505
Amounts reclassified from accumulated other comprehensive income		114,905	(94,489)	(595,019)	222,359
Comprehensive Income		1,486,617	2,174,826	3,516,319	2,215,864
Balance at end of period		6,305,294	3,045,771	6,305,294	3,045,771
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(458,322)	(2,872,655)	(1,197,281)	(1,915,834)
Other Comprehensive income (loss) before reclassifications		424	353,397	124,124	(1,321,890)
Amounts reclassified from accumulated other comprehensive income		155,066	342,252	770,325	1,060,718
Comprehensive Income		155,490	695,649	894,449	(261,172)
Balance at end of period		$ (302,832)	$ (2,177,006)	$ (302,832)	$ (2,177,006)

[1] Note: The condensed consolidated balance sheet at December 31, 2016 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.