Comprehensive Income (AOCI Rollforward) (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	[1]			$ (1,130,836)
Comprehensive Income		$ 84,901,726	$ 72,894,392	164,420,474	$ 147,568,765
Balance at end of period		(3,475,598)	7,139,902	(3,475,598)	7,139,902
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		279,935	460,925	(44,909)	1,403,899
Other Comprehensive (loss) income before reclassifications		(1,753,823)	300,767	(1,428,979)	(642,207)
Comprehensive Income		(1,753,823)	300,767	(1,428,979)	(642,207)
Balance at end of period		(1,473,888)	761,692	(1,473,888)	761,692
Unrealized gains on available-for-sale securities:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		622,330	10,492,827	829,907	10,868,322
Other Comprehensive (loss) income before reclassifications		232,539	(3,186,497)	(275,809)	626,452
Amounts reclassified from accumulated other comprehensive income		16,076	1,245,234	316,847	(2,943,210)
Comprehensive Income		248,615	(1,941,263)	41,038	(2,316,758)
Balance at end of period		870,945	8,551,564	870,945	8,551,564
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(2,794,347)	(2,149,805)	(1,915,834)	(959,206)
Other Comprehensive (loss) income before reclassifications		(437,811)	(23,549)	(1,675,287)	(1,214,148)
Amounts reclassified from accumulated other comprehensive income		359,503	0	718,466	0
Comprehensive Income		(78,308)	(23,549)	(956,821)	(1,214,148)
Balance at end of period		$ (2,872,655)	$ (2,173,354)	$ (2,872,655)	$ (2,173,354)

[1] Note: The condensed consolidated balance sheet at December 31, 2015 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.