Comprehensive Income (AOCI Rollforward) (Details) - USD ($)		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	[1]	$ 1,910,424,234
Comprehensive Income		99,573,280	$ 79,518,748
Balance at end of period		1,974,771,538
Accumulated other comprehensive income (loss), end of period		745,234	(1,892,082)
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(2,862,999)	(44,909)
Other Comprehensive income (loss) before reclassifications		188,590	324,844
Comprehensive Income		188,590	324,844
Balance at end of period		(2,674,409)	279,935
Unrealized gains on available-for-sale securities:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		2,788,975	829,907
Other Comprehensive income (loss) before reclassifications		1,575,383	(508,348)
Amounts reclassified from accumulated other comprehensive income		(164,718)	300,771
Comprehensive Income		1,410,665	(207,577)
Balance at end of period		4,199,640	622,330
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(1,197,281)	(1,915,834)
Other Comprehensive income (loss) before reclassifications		147,318	(1,237,475)
Amounts reclassified from accumulated other comprehensive income		269,966	358,962
Comprehensive Income		417,284	(878,513)
Balance at end of period		$ (779,997)	$ (2,794,347)

[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.