Comprehensive Income (Reclassification Out of Accumulated Other Comprehensive Income) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for income taxes									$ (75,731,395)	$ (84,163,850)	$ (125,004,782)
Total reclassifications for the period	$ 99,547,000	$ 111,898,000	$ 108,959,000	$ 104,280,000	$ 106,275,000	$ 111,336,000	$ 109,024,000	$ 111,249,000	424,683,939	437,883,097	406,791,922
Amounts Reclassified from Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period									382,584	1,682,208	(264,257)
Amounts Reclassified from Other Comprehensive Income | Unrealized gains on available-for-sale debt securities
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Realized gain (loss)									484,283	2,006,235	933,778
Provision for income taxes									(101,699)	(421,309)	(326,822)
Total reclassifications for the period									382,584	1,584,926	606,956
Amounts Reclassified from Other Comprehensive Income | Unrealized gains (losses) on derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Realized gain (loss)									0	123,142	(1,340,329)
Provision for income taxes									0	(25,860)	469,116
Total reclassifications for the period									$ 0	$ 97,282	$ (871,213)