Comprehensive Income (AOCI Rollforward) (Details) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	[1]			$ 11,313,015
Comprehensive Income		$ 69,430,897	$ 68,956,915	216,999,662	$ 209,792,103
Balance at end of period		(1,761,626)	14,137,766	(1,761,626)	14,137,766
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		761,692	2,175,183	1,403,899	2,507,922
Other Comprehensive (loss) income before reclassifications		(396,685)	(269,392)	(1,038,892)	(602,131)
Amounts reclassified from accumulated other comprehensive income		0	0	0	0
Comprehensive Income		(396,685)	(269,392)	(1,038,892)	(602,131)
Balance at end of period		365,007	1,905,791	365,007	1,905,791
Unrealized gains on available-for-sale securities:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		8,551,564	15,342,551	10,868,322	19,467,441
Other Comprehensive (loss) income before reclassifications		(6,353,685)	(1,604,338)	(5,727,233)	1,788,502
Amounts reclassified from accumulated other comprehensive income		(1,321,982)	(1,506,238)	(4,265,192)	(9,023,968)
Comprehensive Income		(7,675,667)	(3,110,576)	(9,992,425)	(7,235,466)
Balance at end of period		875,897	12,231,975	875,897	12,231,975
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(2,173,354)	0	(959,206)	0
Other Comprehensive (loss) income before reclassifications		(1,113,648)	0	(2,327,796)	0
Amounts reclassified from accumulated other comprehensive income		284,472	0	284,472	0
Comprehensive Income		(829,176)	0	(2,043,324)	0
Balance at end of period		$ (3,002,530)	$ 0	$ (3,002,530)	$ 0

[1] Note: The condensed consolidated balance sheet at December 31, 2014 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.