Investments (Schedule of Amortized Cost, Unrealized Gains And Losses, And Market Value of Investment Securities) (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	$ 534,518,281	$ 551,557,527
Cost	205,008,466	98,427,114
Unrealized Gains	5,433,063	6,146,311
Unrealized Losses	(747,262)	(4,869,531)
Market Value	209,694,267	99,703,894
Investments and Cash	744,212,548	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	10,011,046	3,013,482
Unrealized Gains	1,799	0
Unrealized Losses	(2,235)	(2,622)
Market Value	10,010,610	3,010,860
Short-term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	6,773,386	1,512,405
Unrealized Gains	0	0
Unrealized Losses	(7,972)	(390)
Market Value	6,765,414	1,512,015	$ 6,765,414
Short-term Investments [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	125,217	24,480
Unrealized Gains	0	0
Unrealized Losses	0	0
Market Value	125,217	24,480
Short-term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	5,235,438
Unrealized Gains	99,140
Unrealized Losses	(66)
Market Value	5,334,512
Long-Term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	1,970,096
Unrealized Gains	0
Unrealized Losses	(2,002)
Market Value	1,968,094
Long-Term Investments [Member] | Common Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	10,978,179	17,395,641
Unrealized Gains	3,111,060	4,078,912
Unrealized Losses	(395,605)	(1,019,749)
Market Value	13,693,634	20,454,804
Long-Term Investments [Member] | Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	39,536,844	76,481,106
Unrealized Gains	2,206,543	2,067,399
Unrealized Losses	(339,382)	(3,846,770)
Market Value	41,404,005	74,701,735
Long-Term Investments [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	378,260
Unrealized Gains	14,521
Unrealized Losses	0
Market Value	392,781
Fair Value, Inputs, Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	534,518,281	551,557,527
Investments and Cash	720,133,918	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	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	125,217	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	13,693,634	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	41,404,005	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	392,781
Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash & Cash Equivalents	0	0
Investments and Cash	24,078,630	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	10,010,610	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	6,765,414
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	5,334,512
Fair Value, Inputs, Level 2 [Member] | Long-Term Investments [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	1,968,094
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	$ 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