Comprehensive Income (AOCI Rollforward) (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	[1]			$ 1,910,424,234
Comprehensive Income		$ 90,971,869	$ 84,901,726	190,545,149	$ 164,420,474
Balance at end of period		2,003,936,423		2,003,936,423
Accumulated other comprehensive income (loss), end of period		3,181,156	(3,475,598)	3,181,156	(3,475,598)
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(2,674,409)	279,935	(2,862,999)	(44,909)
Other Comprehensive income (loss) before reclassifications		1,495,210	(1,753,823)	1,683,800	(1,428,979)
Comprehensive Income		1,495,210	(1,753,823)	1,683,800	(1,428,979)
Balance at end of period		(1,179,199)	(1,473,888)	(1,179,199)	(1,473,888)
Unrealized gains on available-for-sale securities:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		4,199,640	622,330	2,788,975	829,907
Other Comprehensive income (loss) before reclassifications		1,164,243	232,539	2,739,626	(275,809)
Amounts reclassified from accumulated other comprehensive income		(545,206)	16,076	(709,924)	316,847
Comprehensive Income		619,037	248,615	2,029,702	41,038
Balance at end of period		4,818,677	870,945	4,818,677	870,945
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		(779,997)	(2,794,347)	(1,197,281)	(1,915,834)
Other Comprehensive income (loss) before reclassifications		(23,617)	(437,811)	123,701	(1,675,287)
Amounts reclassified from accumulated other comprehensive income		345,292	359,503	615,258	718,466
Comprehensive Income		321,675	(78,308)	738,959	(956,821)
Balance at end of period		$ (458,322)	$ (2,872,655)	$ (458,322)	$ (2,872,655)

[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.