Fair Value Measurements (Details) (USD $)					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Convertible senior notes	Dec. 31, 2013 Convertible senior notes	Sep. 30, 2014 Significant Other Observable Inputs (Level 2)	Sep. 30, 2013 Significant Other Observable Inputs (Level 2)	Sep. 30, 2014 Significant Other Observable Inputs (Level 2)	Sep. 30, 2013 Significant Other Observable Inputs (Level 2)	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2014 Measured on a recurring basis Fair Value	Dec. 31, 2013 Measured on a recurring basis Fair Value	Sep. 30, 2014 Measured on a recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1)	Dec. 31, 2013 Measured on a recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1)	Sep. 30, 2014 Measured on a recurring basis Significant Other Observable Inputs (Level 2)	Dec. 31, 2013 Measured on a recurring basis Significant Other Observable Inputs (Level 2)	Sep. 30, 2014 Restricted [Member] Measured on a recurring basis Fair Value	Sep. 30, 2014 Restricted [Member] Measured on a recurring basis Significant Other Observable Inputs (Level 2)	Sep. 30, 2014 Unrestricted [Member]	Sep. 30, 2014 Unrestricted [Member] Measured on a recurring basis Fair Value	Dec. 31, 2013 Unrestricted [Member] Measured on a recurring basis Fair Value	Sep. 30, 2014 Unrestricted [Member] Measured on a recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1)	Dec. 31, 2013 Unrestricted [Member] Measured on a recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1)	Sep. 30, 2014 Unrestricted [Member] Measured on a recurring basis Significant Other Observable Inputs (Level 2)	Dec. 31, 2013 Unrestricted [Member] Measured on a recurring basis 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
Marketable Securities, Unrealized Gain (Loss)									0	0	0	0
Debt Instrument, Face Amount		400,000,000	338,900,000	400,000,000
Available-for-sale marketable securities:
U.S. government and government agency obligations																						51,129,000	107,521,000			51,129,000	107,521,000
Corporate bonds																						695,592,000	369,193,000			695,592,000	369,193,000
Municipal bonds																						42,842,000	36,921,000			42,842,000	36,921,000
Commercial paper																							23,944,000				23,944,000
International government agency obligations																							2,008,000				2,008,000
Certificates of deposit																							7,514,000				7,514,000
Equity securities																			54,431,000	54,431,000		5,099,000	1,166,000	5,099,000	1,166,000
Total fair value of available-for-sale marketable securities	849,093,000	548,267,000											849,093,000	548,267,000	5,099,000	1,166,000	843,994,000	547,101,000			794,662,000	794,662,000		5,099,000		789,563,000
Convertible Debt [Abstract]
Interest rate, stated percentage			1.875%	1.875%
Fair value of the outstanding notes																	$ 1,433,800,000	$ 1,327,200,000