Investments (Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value of Investment Securities) (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	$ 569,896,553	$ 497,429,804
Cost	101,584,848	97,923,092
Unrealized Gains	14,464,744	17,855,921
Unrealized Losses	(1,308,492)	(1,135,425)
Market Value	114,741,100	114,643,588
Investments and Cash	684,637,653	612,073,392
Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	454	1,021
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	454	1,021
Long-Term Investments [Member] | Common Stock
Schedule of Available-for-sale Securities [Line Items]
Cost	18,690,052	17,069,742
Unrealized Gains	5,639,978	7,933,717
Unrealized Losses	(644,310)	(355,008)
Market Value	23,685,720	24,648,451
Long-Term Investments [Member] | Mutual Funds – Equity
Schedule of Available-for-sale Securities [Line Items]
Cost	82,894,342	80,852,329
Unrealized Gains	8,824,766	9,922,204
Unrealized Losses	(664,182)	(780,417)
Market Value	91,054,926	89,994,116
Fair Value, Inputs, Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	569,896,553	497,429,804
Investments and Cash	684,637,653	612,073,392
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	454	1,021
Fair Value, Inputs, Level 1 [Member] | Long-Term Investments [Member] | Common Stock
Schedule of Available-for-sale Securities [Line Items]
Market Value	23,685,720	24,648,451
Fair Value, Inputs, Level 1 [Member] | Long-Term Investments [Member] | Mutual Funds – Equity
Schedule of Available-for-sale Securities [Line Items]
Market Value	91,054,926	89,994,116
Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	0	0
Investments and Cash	0	0
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] | Common Stock
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
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	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] | 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] | Common Stock
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
Schedule of Available-for-sale Securities [Line Items]
Market Value	$ 0	$ 0