Fair Value Measurements (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 31, 2011
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	$ 711,915,000	$ 548,267,000
Convertible Debt [Abstract]
Total convertible senior notes - par		400,000,000
Liabilities, Current	654,660,000	298,835,000
Convertible senior notes
Convertible Debt [Abstract]
Total convertible senior notes - par	169,400,000	400,000,000		400,000,000.0
Interest rate, stated percentage	1.875%	1.875%		1.875%
Fair value of the outstanding notes	819,800,000	1,327,200,000
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
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of marketable securities held			1
Available-for-sale marketable securities:
Marketable Securities, Unrealized Gain (Loss)	0	0
Unrestricted
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	620,476,000	548,267,000
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	7,379,000	1,166,000
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	704,536,000	547,101,000
Measured on a recurring basis | Unrestricted | Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale marketable securities:
Available-for-sale Securities, Equity Securities	7,379,000	1,166,000
Total fair value of available-for-sale marketable securities	7,379,000
Measured on a recurring basis | Unrestricted | Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
U.S. government and government agency obligations	28,553,000	107,521,000
Commercial Paper, at Carrying Value		23,944,000
Municipal Debt Securities, at Carrying Value	37,038,000	36,921,000
Available-for-sale Securities, Equity Securities	547,506,000	369,193,000
International Government Obligations Fair Value Disclosure		2,008,000
Certificates of Deposit, at Carrying Value		7,514,000
Total fair value of available-for-sale marketable securities	613,097,000
Measured on a recurring basis | Restricted | Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Available-for-sale Securities, Equity Securities	91,439,000
Fair Value | Measured on a recurring basis
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	711,915,000	548,267,000
Fair Value | Measured on a recurring basis | Unrestricted
Available-for-sale marketable securities:
U.S. government and government agency obligations	28,553,000	107,521,000
Financial Instruments, Owned, Corporate Debt, at Fair Value	547,506,000	369,193,000
Commercial Paper, at Carrying Value		23,944,000
Municipal Debt Securities, at Carrying Value	37,038,000	36,921,000
Available-for-sale Securities, Equity Securities	7,379,000	1,166,000
International Government Obligations Fair Value Disclosure		2,008,000
Certificates of Deposit, at Carrying Value		7,514,000
Total fair value of available-for-sale marketable securities	620,476,000
Fair Value | Measured on a recurring basis | Restricted
Available-for-sale marketable securities:
Available-for-sale Securities, Equity Securities	91,439,000
Warrant Transactions
Convertible Debt [Abstract]
Other Liabilities, Fair Value Disclosure	$ 87,500,000