Investments (Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value of Investment Securities) (Details) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	$ 559,645,625	$ 546,477,075
Cost	231,686,980	222,624,828
Unrealized Gains	6,880,406	5,209,434
Unrealized Losses	(419,421)	(918,703)
Market Value	238,147,965	226,915,559
Investments and Cash	797,793,590	773,392,634
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] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	17,017,432	14,003,644
Unrealized Gains	0	0
Unrealized Losses	(21,362)	(10,164)
Market Value	16,996,070	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	26,322,271	26,116,681
Short-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3,058,352	6,706,721
Unrealized Gains	0	0
Unrealized Losses	(3,632)	(8,339)
Market Value	3,054,720	6,698,382
Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	262,742	212,653
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	262,742	212,653
Short-term Investments [Member] | Mutual Funds – Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	26,458,425
Unrealized Gains	41,908
Unrealized Losses	(178,062)
Market Value	26,322,271
Long-Term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	6,059,283	5,519,668
Unrealized Gains	0	661
Unrealized Losses	(9,093)	(9,539)
Market Value	6,050,190	5,510,790
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
Long-Term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	10,823,853	1,955,292
Unrealized Gains	9,342	0
Unrealized Losses	(3,650)	(6,736)
Market Value	10,829,545	1,948,556
Long-Term Investments [Member] | Common Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	9,879,067	9,825,550
Unrealized Gains	3,613,008	3,349,962
Unrealized Losses	(186,812)	(326,505)
Market Value	13,305,263	12,849,007
Long-Term Investments [Member] | Mutual Funds – Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	27,382,364
Unrealized Gains	3,206,612
Unrealized Losses	(5,223)
Market Value	30,583,753
Long-Term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	745,462	745,462
Unrealized Gains	9,536	360
Unrealized Losses	(11,587)	(31,822)
Market Value	743,411	714,000
Fair Value, Inputs, Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	559,645,625	546,477,075
Investments and Cash	734,540,794	719,124,745
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] | 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
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] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	262,742	212,653
Fair Value, Inputs, Level 1 [Member] | Long-Term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0
Fair Value, Inputs, Level 1 [Member] | 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] | Long-Term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0
Fair Value, Inputs, Level 1 [Member] | Long-Term Investments [Member] | Common Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	13,305,263	12,849,007
Fair Value, Inputs, Level 1 [Member] | Long-Term Investments [Member] | Mutual Funds – Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	30,583,753
Fair Value, Inputs, Level 1 [Member] | Long-Term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	743,411	714,000
Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	0	0
Investments and Cash	63,252,796	54,267,889
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] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	16,996,070	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	26,322,271	26,116,681
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	3,054,720	6,698,382
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] | Long-Term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	6,050,190	5,510,790
Fair Value, Inputs, Level 2 [Member] | Long-Term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		0
Fair Value, Inputs, Level 2 [Member] | Long-Term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	10,829,545	1,948,556
Fair Value, Inputs, Level 2 [Member] | 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] | 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] | Long-Term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0
Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	0	0
Investments and Cash	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] | 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] | 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] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Long-Term Investments [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	0
Fair Value, Inputs, Level 3 [Member] | Long-Term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		0
Fair Value, Inputs, Level 3 [Member] | 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] | 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] | 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] | Long-Term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	$ 0	$ 0