Investments (Schedule of Assets or Liabilities, Recurring Fair Value Measurements) (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash & Cash Equivalents	$ 561,999,767	$ 546,477,075
Market Value	230,314,364	226,915,559
Investments and Cash	792,314,131	773,392,634
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash & Cash Equivalents	561,999,767	546,477,075
Investments and Cash	740,850,681	719,124,745
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash & Cash Equivalents	0	0
Investments and Cash	51,463,450	54,267,889
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash & Cash Equivalents	0	0
Investments and Cash	0	0
Short-term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	130,000,000	130,000,000
Short-term Investments [Member] | Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	130,000,000	130,000,000
Short-term Investments [Member] | Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	7,709,586	6,698,382
Short-term Investments [Member] | Corporate Bond Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Corporate Bond Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	7,709,586	6,698,382
Short-term Investments [Member] | Corporate Bond Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	14,026,870	13,993,480
Short-term Investments [Member] | Government Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	14,026,870	13,993,480
Short-term Investments [Member] | Government Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	26,693,214	26,116,681
Short-term Investments [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	26,693,214	26,116,681
Short-term Investments [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Other Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	221,259	212,653
Short-term Investments [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	221,259	212,653
Short-term Investments [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Short-term Investments [Member] | Mutual Funds – Equity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	26,693,214
Other Long-term Investments [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	3,033,780	1,948,556
Other Long-term Investments [Member] | Corporate Bond Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Other Long-term Investments [Member] | Corporate Bond Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	3,033,780	1,948,556
Other Long-term Investments [Member] | Corporate Bond Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Other Long-term Investments [Member] | Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value		5,510,790
Other Long-term Investments [Member] | Government Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value		0
Other Long-term Investments [Member] | Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value		5,510,790
Other Long-term Investments [Member] | Government Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value		0
Other Long-term Investments [Member] | Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value		28,872,010
Other Long-term Investments [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value		28,872,010
Other Long-term Investments [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value		0
Other Long-term Investments [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value		0
Other Long-term Investments [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	14,606,120	12,849,007
Other Long-term Investments [Member] | Common Stocks [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	14,606,120	12,849,007
Other Long-term Investments [Member] | Common Stocks [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Other Long-term Investments [Member] | Common Stocks [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Other Long-term Investments [Member] | Mutual Funds – Equity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	33,234,535
Other Long-term Investments [Member] | Mutual Funds – Equity [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	33,234,535
Other Long-term Investments [Member] | Mutual Funds – Equity [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0
Other Long-term Investments [Member] | Mutual Funds – Equity [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0
Other Long-term Investments [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	789,000	714,000
Other Long-term Investments [Member] | Preferred Stock [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	789,000	714,000
Other Long-term Investments [Member] | Preferred Stock [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	0	0
Other Long-term Investments [Member] | Preferred Stock [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market Value	$ 0	$ 0