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Net Loss Per Share (Details) - USD ($)	3 Months Ended		6 Months Ended
Net Loss Per Share (Details) - USD ($)	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Apr. 03, 2017	Nov. 30, 2015	Nov. 02, 2015	Dec. 10, 2013
Earnings Per Share, Basic and Diluted [Abstract]
Net loss	$ (23,876,000)	$ (16,292,000)	$ (43,643,000)	$ (37,606,000)
Shares used in computing basic and diluted net loss per share (in shares)	84,462,000	83,247,000	84,112,000	83,087,000
Basic and diluted net loss per share (in dollars per share)	$ (0.28)	$ (0.20)	$ (0.52)	$ (0.45)
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	911,000	902,000	835,000	1,004,000
Potential Dilutive Effect of Securities [Abstract]
Conversion of the Notes (in shares)	11,939,000	11,939,000	11,939,000	11,939,000
Conversion of Deerfield Warrants (in shares)	6,470,000	6,470,000	6,470,000	6,470,000
3.25% Convertible Senior Notes
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Stated interest rate	3.25%		3.25%
Debt instrument face amount	$ 40,500,000		$ 40,500,000
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	$ 17,800,000		$ 17,800,000					$ 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	$ 110,700,000		$ 110,700,000			$ 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)	213,000	574,000	252,000	636,000
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)	126,000	121,000	122,000	120,000
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)	572,000	207,000	461,000	248,000