Investments (Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value of Investment Securities) (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 152,252,568	$ 196,926,043
Unrealized Gains	0	10,562,267
Unrealized Losses	(33,160)	(367,837)
Market Value	152,219,408	207,120,473
Short-Term Investments \| Certificates of Deposit
Schedule of Available-for-sale Securities [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
Schedule of Available-for-sale Securities [Line Items]
Cost	15,919,177	12,952,229
Unrealized Gains	0	0
Unrealized Losses	(27,360)	(7,230)
Market Value	15,891,817	12,944,999
Short-Term Investments \| Government Securities
Schedule of Available-for-sale Securities [Line Items]
Cost	6,009,310	9,024,777
Unrealized Gains	0	0
Unrealized Losses	(5,800)	(13,647)
Market Value	6,003,510	9,011,130
Short-Term Investments \| Mutual Funds
Schedule of Available-for-sale Securities [Line Items]
Cost		392,482
Unrealized Gains		1,575
Unrealized Losses		(476)
Market Value		393,581
Short-Term Investments \| Other
Schedule of Available-for-sale Securities [Line Items]
Cost	284,081	188,344
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	284,081	188,344
Long-Term Investments \| Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Cost		3,022,994
Unrealized Gains		0
Unrealized Losses		(4,274)
Market Value		3,018,720
Long-Term Investments \| Mutual Funds
Schedule of Available-for-sale Securities [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
Schedule of Available-for-sale Securities [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
Schedule of Available-for-sale Securities [Line Items]
Cost		1,141,458
Unrealized Gains		40,533
Unrealized Losses		(3,000)
Market Value		$ 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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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.

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-Publisher FASB
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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.

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