Convertible Notes (Details 2) (USD $)	12 Months Ended						12 Months Ended						12 Months Ended	1 Months Ended	12 Months Ended				1 Months Ended		0 Months Ended		12 Months Ended			0 Months Ended		12 Months Ended			0 Months Ended	1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Carrying Amount	Dec. 31, 2012 Carrying Amount	Dec. 31, 2013 Fair Value	Dec. 31, 2012 Fair Value	Dec. 31, 2013 4.75% Convertible Senior Notes due 2015	Dec. 31, 2012 4.75% Convertible Senior Notes due 2015	Dec. 31, 2013 4.75% Convertible Senior Notes due 2015 Carrying Amount	Dec. 31, 2012 4.75% Convertible Senior Notes due 2015 Carrying Amount	Dec. 31, 2013 4.75% Convertible Senior Notes due 2015 Fair Value	Dec. 31, 2012 4.75% Convertible Senior Notes due 2015 Fair Value	Dec. 31, 2013 4.75% Convertible Senior Notes due 2015 Baker Entities	Aug. 31, 2013 Pfizer Convertible Subordinated Note due 2014	Dec. 31, 2013 Pfizer Convertible Subordinated Note due 2014	Dec. 31, 2012 Pfizer Convertible Subordinated Note due 2014	Dec. 31, 2012 Pfizer Convertible Subordinated Note due 2014 Carrying Amount	Dec. 31, 2012 Pfizer Convertible Subordinated Note due 2014 Fair Value	Oct. 31, 2007 Pfizer Convertible Subordinated Note due 2014 Collaborative Research and License Agreement with Pfizer	Aug. 31, 2013 Pfizer Convertible Subordinated Note due 2014 Collaborative Research and License Agreement with Pfizer	Nov. 14, 2013 0.375% convertible senior notes due 2018 and 1.25% convertible senior notes due 2020	Nov. 14, 2013 0.375% Convertible Senior Notes due 2018	Dec. 31, 2013 0.375% Convertible Senior Notes due 2018	Dec. 31, 2013 0.375% Convertible Senior Notes due 2018 Carrying Amount	Dec. 31, 2013 0.375% Convertible Senior Notes due 2018 Fair Value	Nov. 14, 2013 0.375% Convertible Senior Notes due 2018 Baker Entities	Nov. 14, 2013 1.25% Convertible Senior Notes due 2020	Dec. 31, 2013 1.25% Convertible Senior Notes due 2020	Dec. 31, 2013 1.25% Convertible Senior Notes due 2020 Carrying Amount	Dec. 31, 2013 1.25% Convertible Senior Notes due 2020 Fair Value	Nov. 14, 2013 1.25% Convertible Senior Notes due 2020 Baker Entities	Dec. 31, 2012 Pfizer convertible subordinated note due 2013	Feb. 28, 2006 Pfizer convertible subordinated note due 2013 Collaborative Research and License Agreement with Pfizer	Dec. 31, 2012 Pfizer convertible subordinated note due 2013 Collaborative Research and License Agreement with Pfizer
Convertible Notes
Convertible senior notes	$ 661,567,000	$ 322,043,000							$ 84,193,000	$ 322,043,000	$ 556,272,000	$ 798,040,000												$ 301,037,000	$ 448,350,000				$ 276,337,000	$ 454,913,000
Convertible subordinated notes		9,033,000															9,033,000	13,573,000
Long-term debt, noncurrent			661,567,000	331,076,000	1,459,535,000	811,613,000
Interest rate of debt (as a percent)							4.75%	4.75%								0.00%							0.375%					1.25%
Aggregate principal amount of notes																			10,000,000			375,000,000				250,000,000	375,000,000				250,000,000		10,000,000
Number of days within 30 consecutive trading days in which the price of the entity's common stock must exceed the conversion price for the notes to be converted																					20 days
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible																					30 days
Percentage of the closing sales price of common stock that the conversion price must exceed in order for the notes to be convertible (as a percent)																					130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period																					5 days
Number of consecutive trading days before five consecutive business days during the note measurement period																					5 days
Percentage of the trading price to the product of the last reported sale price of the common stock and the conversion rate, maximum (as a percent)																					98.00%
Conversion ratio, number of shares per principal amount							0.1139601																0.0193207					0.0193207
Conversion price per share (in dollars per share)							$ 8.78													$ 6.84			$ 51.76					$ 51.76						$ 6.84
Repurchase price as a percentage of principal							100.00%																100.00%					100.00%
Liability on notes on the date of issuance							118,600,000																299,400,000					274,800,000
Equity component in convertible notes							381,400,000																75,600,000					100,200,000
Carrying value of notes							100,700,000
Aggregate principal amount of notes that can be converted into common stock														10,000,000																		10,000,000
Common stock issued in exchange of notes (in shares)							21,208,303								1,025,641	1,461,496
Aggregate principal amount of notes exchanged							186,000,000
Cash used to fund redemption of notes	499,994,000						11,500,000
Debt exchange expense							11,500,000
Net proceeds from issuance of notes	728,696,000												500,000,000
Reduction in additional paid-up capital							381,400,000
Repurchase of notes							117,300,000
Loss on debt repurchase	$ (17,934,000)						$ 17,900,000