Investments (Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value of Investment Securities) (Details) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	$ 499,493,964	$ 551,557,527
Cost	217,452,974	98,427,114
Unrealized Gains	5,454,908	6,146,311
Unrealized Losses	(4,114,992)	(4,869,531)
Market Value	218,792,890	99,703,894
Investments and Cash	718,286,854	651,261,421
Short-term Investments [Member] | Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	130,000,000
Unrealized Gains	0
Unrealized Losses	0
Market Value	130,000,000
Short-term Investments [Member] | US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	10,022,758	3,013,482
Unrealized Gains	4,372	0
Unrealized Losses	0	(2,622)
Market Value	10,027,130	3,010,860
Short-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		1,512,405
Unrealized Gains		0
Unrealized Losses		(390)
Market Value		1,512,015
Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	41,736	24,480
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	41,736	24,480
Short-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	5,172,416
Unrealized Gains	94,250
Unrealized Losses	0
Market Value	5,266,666
Long-Term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	1,984,889
Unrealized Gains	1,730
Unrealized Losses	0
Market Value	1,986,619
Long-Term Investments [Member] | Common Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	13,987,384	17,395,641
Unrealized Gains	3,724,622	4,078,912
Unrealized Losses	(823,075)	(1,019,749)
Market Value	16,888,931	20,454,804
Long-Term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	55,994,531	76,481,106
Unrealized Gains	1,619,354	2,067,399
Unrealized Losses	(3,291,917)	(3,846,770)
Market Value	54,321,968	74,701,735
Long-Term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	249,260
Unrealized Gains	10,580
Unrealized Losses	0
Market Value	259,840
Fair Value, Inputs, Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	499,493,964	551,557,527
Investments and Cash	701,006,439	646,738,546
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
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	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
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	41,736	24,480
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] | 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	16,888,931	20,454,804
Fair Value, Inputs, Level 1 [Member] | Long-Term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	54,321,968	74,701,735
Fair Value, Inputs, Level 1 [Member] | Long-Term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	259,840
Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	0	0
Investments and Cash	17,280,415	4,522,875
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
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	10,027,130	3,010,860
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value		1,512,015
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] | Short-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	5,266,666
Fair Value, Inputs, Level 2 [Member] | Long-Term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	1,986,619
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 [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	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
Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member] | US Government Agencies Debt Securities [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
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] | Short-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
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 [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	0	$ 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