Investments (Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value of Investment Securities) (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Cost	$ 282,808,432	$ 196,926,043
Unrealized Gains	56	10,562,267
Unrealized Losses	(753,437)	(367,837)
Market Value	282,055,051	207,120,473
Short-Term Investments \| Certificates of Deposit
Debt Securities, Available-for-sale [Line Items]
Cost	130,000,000	130,000,000
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	130,000,000	130,000,000
Short-Term Investments \| Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Cost	4,998,499	12,952,229
Unrealized Gains	0	0
Unrealized Losses	(4,481)	(7,230)
Market Value	4,994,018	12,944,999
Short-Term Investments \| Government Securities
Debt Securities, Available-for-sale [Line Items]
Cost	6,699,555	9,024,777
Unrealized Gains	0	0
Unrealized Losses	(7,606)	(13,647)
Market Value	6,691,949	9,011,130
Short-Term Investments \| Mutual Funds
Debt Securities, Available-for-sale [Line Items]
Cost		392,482
Unrealized Gains		1,575
Unrealized Losses		(476)
Market Value		393,581
Short-Term Investments \| Other
Debt Securities, Available-for-sale [Line Items]
Cost	1,937,574	188,344
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	1,937,574	188,344
Long-Term Investments \| Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Cost	62,619,934	3,022,994
Unrealized Gains	56	0
Unrealized Losses	(226,917)	(4,274)
Market Value	62,393,073	3,018,720
Long-Term Investments \| Government Securities
Debt Securities, Available-for-sale [Line Items]
Cost	58,671,384
Unrealized Gains	0
Unrealized Losses	(339,765)
Market Value	58,331,619
Long-Term Investments \| Mutual Funds
Debt Securities, Available-for-sale [Line Items]
Cost		29,306,540
Unrealized Gains		5,440,344
Unrealized Losses		(65,547)
Market Value		34,681,337
Long-Term Investments \| Common Stocks
Debt Securities, Available-for-sale [Line Items]
Cost	40,000	10,897,219
Unrealized Gains	0	5,079,815
Unrealized Losses	0	(273,663)
Market Value	40,000	15,703,371
Long-Term Investments \| Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Cost	17,841,486	1,141,458
Unrealized Gains	0	40,533
Unrealized Losses	(174,668)	(3,000)
Market Value	$ 17,666,818	$ 1,178,991

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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