Fair Value Measurements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2011
Available-for-sale marketable securities:
Total fair value of available-for-sale marketable securities	$ 868,282,000	$ 711,915,000
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	91,400,000	0
Convertible Debt [Abstract]
Liabilities, Current	$ 811,162,000	654,660,000
Convertible senior notes
Convertible Debt [Abstract]
Convertible Debt, Noncurrent		$ 169,400,000
Interest rate, stated percentage	1.875%	1.875%		1.875%
Fair value of the outstanding notes	$ 72,800,000	$ 819,800,000
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)
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	548,267,000	620,476,000
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	31,466,000	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	836,816,000	704,536,000
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	31,466,000	7,379,000
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:
Financial Instruments, Owned, Corporate Debt, at Fair Value	767,683,000	547,506,000
U.S. government and government agency obligations	51,209,000	28,553,000
Municipal Debt Securities, at Carrying Value	17,924,000	37,038,000
Total fair value of available-for-sale marketable securities		613,097,000
Measured on a recurring basis | Restricted [Member]
Available-for-sale marketable securities:
Available-for-sale Securities, Equity Securities		91,439,000
Measured on a recurring basis | Restricted [Member] | 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	868,282,000	711,915,000
Fair Value | Measured on a recurring basis | Unrestricted
Available-for-sale marketable securities:
Financial Instruments, Owned, Corporate Debt, at Fair Value	767,683,000	547,506,000
U.S. government and government agency obligations	51,209,000	28,553,000
Municipal Debt Securities, at Carrying Value	17,924,000	37,038,000
Available-for-sale Securities, Equity Securities	$ 31,466,000	7,379,000
Total fair value of available-for-sale marketable securities		$ 620,476,000