Summary of Significant Accounting Policies (Details) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) shares	Jun. 30, 2014 USD ($) shares	Jun. 30, 2015 USD ($) Employee shares	Jun. 30, 2014 USD ($) shares	Mar. 31, 2015 USD ($)
Summary of Significant Accounting Policies [Abstract]
Number of employees to receive severance payments | Employee			12
Proceeds from sale of property and equipment			$ 260	$ 0
Loss from sale and disposal of long-lived assets			(84)	0
Number of shares of common stock potentially issuable upon the exercise of stock options and warrants (in shares) | shares	21,300	20,900
Potential common stock issuable upon exercise of stock options and warrants (in shares) | shares	21,300	16,400
Numerator [Abstract]
Net loss as reported	$ (11,326)	$ (10,623)	(23,505)	(22,099)
Less: income from change in fair value of warrant liability	(469)	(1,447)	(438)	(1,820)
Numerator for diluted net loss per common share	$ (11,795)	$ (12,070)	$ (23,943)	$ (23,919)
Denominator [Abstract]
Basic weighted average common shares outstanding (in shares) | shares	85,753	85,061	85,671	84,766
Dilutive common shares from assumed warrant exercises (in shares) | shares	0	821	0	1,345
Diluted weighted average common shares outstanding (in shares) | shares	85,753	85,882	85,671	86,111
September 2013 Severance and Retention Benefits Plan [Member]
Restructuring Cost and Reserve [Line Items]
Employee severance cost			$ 2,900
Accrued severance cost amount					$ 1,100
Severance and retention benefits paid	$ 1,800
Severance and retention benefits to be paid in future periods	1,100		$ 1,100
September 2013 Severance and Retention Benefits Plan [Member] | Research and Development Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Severance and retention benefits paid	900
September 2013 Severance and Retention Benefits Plan [Member] | Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Severance and retention benefits paid	$ 900