Investments (Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value of Investment Securities) (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 220,613,911	$ 222,624,828
Unrealized Gains	10,199,838	5,209,434
Unrealized Losses	(499,385)	(918,703)
Market Value	230,314,364	226,915,559
Short-term Investments [Member] | Certificates of Deposit [Member]
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 [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,700,108	6,706,721
Unrealized Gains	9,478	0
Unrealized Losses	0	(8,339)
Market Value	7,709,586	6,698,382
Short-term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	14,041,499	14,003,644
Unrealized Gains	0	0
Unrealized Losses	(14,629)	(10,164)
Market Value	14,026,870	13,993,480
Short-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		26,326,674
Unrealized Gains		27,459
Unrealized Losses		(237,452)
Market Value	26,693,214	26,116,681
Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	221,259	212,653
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	221,259	212,653
Short-term Investments [Member] | Mutual Funds – Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	26,755,214
Unrealized Gains	56,844
Unrealized Losses	(118,844)
Market Value	26,693,214
Other Long-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3,028,681	1,955,292
Unrealized Gains	5,099	0
Unrealized Losses	0	(6,736)
Market Value	3,033,780	1,948,556
Other Long-term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		5,519,668
Unrealized Gains		661
Unrealized Losses		(9,539)
Market Value		5,510,790
Other Long-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		27,329,164
Unrealized Gains		1,830,992
Unrealized Losses		(288,146)
Market Value		28,872,010
Other Long-term Investments [Member] | Common Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	10,630,324	9,825,550
Unrealized Gains	4,341,708	3,349,962
Unrealized Losses	(365,912)	(326,505)
Market Value	14,606,120	12,849,007
Other Long-term Investments [Member] | Mutual Funds – Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	27,491,364
Unrealized Gains	5,743,171
Unrealized Losses	0
Market Value	33,234,535
Other Long-term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	745,462	745,462
Unrealized Gains	43,538	360
Unrealized Losses	0	(31,822)
Market Value	789,000	714,000
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	130,000,000	130,000,000
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	221,259	212,653
Fair Value, Inputs, Level 1 [Member] | Other Long-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 1 [Member] | Other Long-term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		0
Fair Value, Inputs, Level 1 [Member] | Other Long-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		28,872,010
Fair Value, Inputs, Level 1 [Member] | Other Long-term Investments [Member] | Common Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	14,606,120	12,849,007
Fair Value, Inputs, Level 1 [Member] | Other Long-term Investments [Member] | Mutual Funds – Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	33,234,535
Fair Value, Inputs, Level 1 [Member] | Other Long-term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	789,000	714,000
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	7,709,586	6,698,382
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	14,026,870	13,993,480
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	26,693,214	26,116,681
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 2 [Member] | Other Long-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	3,033,780	1,948,556
Fair Value, Inputs, Level 2 [Member] | Other Long-term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		5,510,790
Fair Value, Inputs, Level 2 [Member] | Other Long-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		0
Fair Value, Inputs, Level 2 [Member] | Other Long-term Investments [Member] | Common Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 2 [Member] | Other Long-term Investments [Member] | Mutual Funds – Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0
Fair Value, Inputs, Level 2 [Member] | Other Long-term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member] | Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Other Long-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Other Long-term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		0
Fair Value, Inputs, Level 3 [Member] | Other Long-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		0
Fair Value, Inputs, Level 3 [Member] | Other Long-term Investments [Member] | Common Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Other Long-term Investments [Member] | Mutual Funds – Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0
Fair Value, Inputs, Level 3 [Member] | Other Long-term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	$ 0	$ 0