Going Concern Uncertainty (Details) - USD ($)	3 Months Ended								5 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Apr. 01, 2014	Jan. 24, 2013
Debt Instrument [Line Items]
Net loss	$ (27,112,000)	$ (20,494,000)	$ (27,438,000)	$ (26,512,000)	$ (34,693,000)	$ (34,918,000)	$ (37,171,000)	$ (34,665,000)		$ (101,556,000)	$ (141,447,000)	$ (162,141,000)
Accumulated deficit	(711,461,000)				(609,905,000)				$ (711,461,000)	(711,461,000)	(609,905,000)
Net cash used in operating activities										(64,534,000)	(85,115,000)	(118,113,000)
Cash and cash equivalents and marketable securities available for sale	64,000,000								64,000,000	64,000,000
Proceeds from issuance of common stock									4,800,000	0	0	59,209,000
Convertible debt exchanged										$ 30,575,000	$ 0	$ 20,147,000
Percentage workforce reduction										20.00%
Inducement Shares
Debt Instrument [Line Items]
Inducement shares (in shares)										4,550,208
2018 Notes | Inducement Shares
Debt Instrument [Line Items]
Inducement shares (in shares)												160,670
Convertible Senior Subordinated Notes | Early Conversion Payment
Debt Instrument [Line Items]
Common stock issued upon early conversion of senior convertible notes (in shares)										9,022,954	0	2,743,475
Convertible Senior Subordinated Notes | 2018 Notes
Debt Instrument [Line Items]
Convertible debt	32,485,000				61,632,000				32,485,000	$ 32,485,000	$ 61,632,000			$ 125,000,000.0
Convertible Senior Subordinated Notes | 2018 Notes | Early Conversion Payment
Debt Instrument [Line Items]
Common stock issued upon early conversion of senior convertible notes (in shares)												2,409,964
Convertible Senior Subordinated Notes | 2019 Notes
Debt Instrument [Line Items]
Convertible debt	$ 148,073,000				$ 149,500,000				$ 148,073,000	$ 148,073,000	$ 149,500,000		$ 149,500,000.0