Comprehensive Income (Reclassification Out of Accumulated Other Comprehensive Income) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for income taxes	$ (84,163,850)	$ (125,004,782)	$ (162,969,497)
Amounts Reclassified from Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	1,682,208	(264,257)	(1,182,844)
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)	2,006,235	933,778	320,197
Provision for income taxes	(421,309)	(326,822)	(112,069)
Total reclassifications for the period	1,584,926	606,956	208,128
Amounts Reclassified from Other Comprehensive Income | Unrealized gains (losses) on derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Realized gain (loss)	123,142	(1,340,329)	(2,139,958)
Provision for income taxes	(25,860)	469,116	748,986
Total reclassifications for the period	$ 97,282	$ (871,213)	$ (1,390,972)