Fair Value Measurements (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jan. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	$ 0	$ 0	$ 0	$ 0	$ 91,400,000
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities						$ 711,915,000
Convertible senior notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Debt, Noncurrent	$ 33,300,000		$ 33,300,000			$ 169,400,000
Convertible Debt [Abstract]
Interest rate, stated percentage	1.875%		1.875%			1.875%
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other than Temporary Impairment Losses, Investments	$ 0	0	$ 0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities, Unrealized Gain (Loss)	0	0	0	0
Measured on a recurring basis
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	803,289,000		803,289,000			$ 711,915,000
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	46,124,000		46,124,000			7,379,000
Measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	757,165,000		757,165,000			704,536,000
Convertible Debt [Abstract]
Fair value of the outstanding notes	201,600,000		201,600,000			819,800,000
Restricted [Member] | Measured on a recurring basis
Available-for-sale marketable securities:
Equity securities						91,439,000
Restricted [Member] | Measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Equity securities						91,439,000
Unrestricted [Member]
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	803,289,000		803,289,000			620,476,000
Unrestricted [Member] | Measured on a recurring basis
Available-for-sale marketable securities:
U.S. government and government agency obligations	57,005,000		57,005,000			28,553,000
Corporate bonds	660,389,000		660,389,000			547,506,000
Municipal bonds	39,771,000		39,771,000			37,038,000
Equity securities	46,124,000		46,124,000			7,379,000
Total fair value of available-for-sale marketable securities						620,476,000
Unrestricted [Member] | Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale marketable securities:
Equity securities	46,124,000		46,124,000			7,379,000
Total fair value of available-for-sale marketable securities						7,379,000
Unrestricted [Member] | Measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
U.S. government and government agency obligations	57,005,000		57,005,000			28,553,000
Municipal bonds	39,771,000		39,771,000			37,038,000
Equity securities	660,389,000		660,389,000			547,506,000
Total fair value of available-for-sale marketable securities						613,097,000
Warrant Transactions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities, Fair Value Disclosure	$ 0	$ 0	$ 0	$ 0		$ 87,500,000	$ 0