Stockholders’ (Deficit)/Equity (Details) - USD ($)						1 Months Ended		3 Months Ended		12 Months Ended
	Nov. 13, 2017	Feb. 06, 2017	Jan. 31, 2017	May 06, 2016	Mar. 18, 2016	Mar. 31, 2017	Nov. 30, 2016	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 27, 2017	Jun. 26, 2017	Jul. 02, 2015	Jun. 08, 2015	Jun. 07, 2015	Nov. 03, 2014
Debt Instrument [Line Items]
Net proceeds from private placement										$ 173,802,000	$ 89,845,000	$ 14,268,000
Common stock, shares authorized (in shares)									350,000,000	400,000,000	350,000,000		400,000,000	350,000,000		350,000,000	200,000,000
Proceeds from common stock issued in connection with exercise of stock options										$ 347,000	$ 222,000	1,142,000
Debt conversion amount										4,912,000	137,941,000	40,989,000
Proceeds from common stock issued for interest on notes											$ 2,445,000	$ 0
Common Shares
Debt Instrument [Line Items]
Shares sold in private placement (in shares)										42,030,630	29,948,334
Common stock issued in connection with exercise of warrants (in shares)											2,430,656	189,412
Common stock issued in connection with exercise of stock options (in shares)										99,978	70,185	269,720
Debt conversion expense (in shares)					9,600,000					212,800	12,161,671
Convertible Senior Notes Due 2019
Debt Instrument [Line Items]
Aggregate principal amount (not exceeding)									$ 23,500,000.0	$ 18,603,000	$ 23,500,000.0	$ 159,000,000						$ 200,000,000
Debt conversion amount					$ 79,800,000	$ 4,900,000	$ 55,700,000			4,911,000	$ 135,497,000
Percent of principal converted					50.00%		70.00%
Number of shares issued on conversion of debt (in shares)					35,300,000	1,800,000	20,500,000				56,600,000
Number of shares issued on conversion price excluding share issued for accrued interest (in shares)					25,600,000		17,900,000
Conversion price (in dollars per share)					$ 3.11													$ 3.11
Number of shares issued for accrued interest (in shares)					872,000
Five day average conversion price for accrued interest (in dollars per share)					$ 2.81
Proceeds from common stock issued for interest on notes					$ 2,400,000
Debt conversion expense (in shares)						1,600,000		200,000	2,600,000
Debt conversion, recognized expense					$ 25,600,000		$ 14,500,000
Percent of outstanding aggregate principal amount converted							70.00%
Shares issued, representing conversion price pursuant to existing terms (in shares)							17,900,000
Additional interest expense from acceleration of deferred debt costs							$ 2,000,000			$ 1,300,000	$ 6,700,000	12,900,000
Debt conversion, recognized expense (in shares)							2,600,000
Debt conversion											135,500,000
June 2012 Equity Sales Agreement
Debt Instrument [Line Items]
Net proceeds from private placement											$ 11,300,000	$ 1,000,000
Common stock issued in connection with exercise of warrants (in shares)											2,430,656	189,412
Common stock issued in connection with exercise of stock options (in shares)												269,720
Proceeds from common stock issued in connection with exercise of stock options												$ 1,100,000
Shelf Registration
Debt Instrument [Line Items]
Aggregate principal amount (not exceeding)															$ 250,000,000
Private Placement
Debt Instrument [Line Items]
Shares sold in private placement (in shares)				29,948,334
Net proceeds from private placement				$ 89,800,000
Shares issued (in dollars per share)				$ 3.00
Public stock offering
Debt Instrument [Line Items]
Shares sold in private placement (in shares)	21,705,426		20,325,204
Net proceeds from private placement	$ 52,200,000	$ 121,600,000
Shares issued (in dollars per share)	$ 2.58		$ 6.15
Cantor Fitzgerald & Co. | June 2012 Equity Sales Agreement
Debt Instrument [Line Items]
Shares sold in private placement (in shares)												3,435,998
Net proceeds from private placement												$ 14,700,000
Share price, average (in dollars per share)												$ 4.27
Attorney fees												$ 400,000