Comprehensive Income (AOCI Rollforward) (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 2,049,518,261	$ 1,910,424,234	$ 1,722,516,761
Comprehensive income	435,732,103	415,256,610	347,450,807
Ending balance	1,861,751,660	2,049,518,261	1,910,424,234
Accumulated other comprehensive income (loss), end of period	(1,600,338)	7,193,383	(1,271,305)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	645,030	(2,862,999)	(44,909)
Other comprehensive income (loss) before reclassifications	(2,319,917)	3,508,029	(2,818,090)
Comprehensive income	(2,319,917)	3,508,029	(2,818,090)
Ending balance	(1,674,887)	645,030	(2,862,999)
Unrealized gains(losses) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	6,626,379	2,788,975	829,907
ASU 2016-01 adoption impact	(6,642,727)	0	0
Other comprehensive income (loss) before reclassifications	1,675,823	4,444,360	2,167,196
Amounts reclassified from accumulated other comprehensive income	(1,584,926)	(606,956)	(208,128)
Comprehensive income	(6,551,830)	3,837,404	1,959,068
Ending balance	74,549	6,626,379	2,788,975
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(78,026)	(1,197,281)	(1,915,834)
Other comprehensive income (loss) before reclassifications	175,308	248,042	(672,419)
Amounts reclassified from accumulated other comprehensive income	(97,282)	871,213	1,390,972
Comprehensive income	78,026	1,119,255	718,553
Ending balance	$ 0	$ (78,026)	$ (1,197,281)

Reclassification from Accumulated Other Comprehensive Income, Accounting Standards Update, Current Period, Net of Tax

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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