Comprehensive Income (Reclassification Out of Accumulated Other Comprehensive Income) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Taxes	$ (125,004,782)	$ (162,969,497)	$ (145,121,597)
Amounts Reclassified from Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(264,257)	(1,182,844)	3,822,086
Amounts Reclassified from Other Comprehensive Income | Unrealized gains and (losses) on available-for-sale securities
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Realized gain (loss)	933,778	320,197	6,960,881
Provision for Income Taxes	(326,822)	(112,069)	(2,436,308)
Total reclassifications for the period	606,956	208,128	4,524,573
Amounts Reclassified from Other Comprehensive Income | Unrealized gains (losses) on derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Realized gain (loss)	(1,340,329)	(2,139,958)	(1,080,750)
Provision for Income Taxes	469,116	748,986	378,263
Total reclassifications for the period	$ (871,213)	$ (1,390,972)	$ (702,487)