Common Stock Warrant Liability (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jul. 22, 2015	Dec. 31, 2014	Feb. 22, 2011
Estimated fair value of warrants accounted for as derivative liabilities [Abstract]
Fair value of warrants	$ 820			$ 1,258
Number of warrant shares potentially issuable (in shares)	13,200,000
Proceeds from exercise of warrants	$ 0	$ 423
February 2011 Warrants [Member]
Estimated fair value of warrants accounted for as derivative liabilities [Abstract]
Warrants issuance date	Feb. 22, 2011
Warrants expiration date	Feb. 22, 2016
Fair value of warrants	$ 800				$ 8,000
Number of warrant shares potentially issuable (in shares)	4,600,000
Exercise price of warrants (in dollars per share)	$ 1.50
Exercise of warrants by warrant holders to purchase common stock (in shares)	0	282,350
Proceeds from exercise of warrants		$ 400
February 2011 Warrants [Member] | Subsequent Event [Member]
Estimated fair value of warrants accounted for as derivative liabilities [Abstract]
Exercise price of warrants (in dollars per share)			$ 0.19