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Net Loss Per Share (Details) - USD ($)	3 Months Ended		6 Months Ended
Net Loss Per Share (Details) - USD ($)	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Apr. 03, 2017	Nov. 30, 2015	Nov. 02, 2015	Dec. 10, 2013
Earnings Per Share, Basic and Diluted [Abstract]
Net loss	$ (16,292,000)	$ (66,837,000)	$ (37,606,000)	$ (114,507,000)
Shares used in computing basic and diluted net loss per share (in shares)	83,247,000	82,072,000	83,087,000	79,368,000
Basic and diluted net loss per share (in dollars per share)	$ (0.20)	$ (0.81)	$ (0.45)	$ (1.44)
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	902,000	2,193,000	1,004,000	1,623,000
Potential Dilutive Effect of Securities [Abstract]
Conversion of the Notes (in shares)	11,939,000	14,767,000	11,939,000	14,767,000
Conversion of Deerfield Warrants (in shares)	6,470,000	0	6,470,000	0
Facility Agreement \| Deerfield Warrants \| Common Stock
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Warrants issued (in shares)					6,470,000
Exercise price of warrants issued (in dollars per share)					$ 9.23
Convertible Debt \| 2.25% Convertible Senior Notes
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Convertible notes	$ 18,300,000		$ 18,300,000					$ 86,300,000
Stated interest rate	2.25%		2.25%					2.25%
Debt instrument face amount								$ 86,250,000
Convertible Debt \| 3.25% Convertible Senior Notes
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Convertible notes	$ 105,500,000		$ 105,500,000			$ 125,000,000
Stated interest rate							3.25%
Debt instrument face amount							$ 125,000,000.0
Secured Debt \| Facility Agreement
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Stated interest rate	6.87%		6.87%
Debt instrument face amount					$ 120,000,000.0
Common stock options
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	574,000	1,620,000	636,000	1,193,000
Restricted stock awards
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	121,000	135,000	120,000	131,000
Restricted stock units
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	207,000	438,000	248,000	299,000