Commitments and Contingencies - Related-Party Transactions (Details)				1 Months Ended					12 Months Ended
	Jan. 10, 2014 person shares	Sep. 30, 2013 USD ($) shares	May 07, 2013 USD ($) $ / shares shares	Dec. 31, 2014 shares	Feb. 28, 2014 shares	Nov. 30, 2012 USD ($) $ / shares shares	Nov. 30, 2012 person $ / shares shares	Nov. 30, 2011 USD ($) person $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares
Related Party Transactions
Warrant to purchase common stock									51,709,460
Proceeds from exercise of warrants | $									$ 2,000,000	$ 1,888,000	$ 7,534,000
Proceeds from issuance of common stock in lieu of director board and committee fees | $									$ 172,000	$ 122,000	$ 82,000
Series E Convertible Preferred Stock
Related Party Transactions
Conversion of preferred stock to common, shares											424,000
Series D Convertible Preferred Stock
Related Party Transactions
Preferred stock, shares issued	1,124,260
Number of people | person	1
Conversion of preferred stock to common, shares											1,124,000
Common Stock | Series E Convertible Preferred Stock
Related Party Transactions
Conversion of preferred stock to common, shares											8,485,000
Common Stock | Series D Convertible Preferred Stock
Related Party Transactions
Conversion of preferred stock to common, shares											6,266,000
Pillar I
Related Party Transactions
Shares issued on exercise of warrants during the period									1,370,000		1,575,758
Proceeds from exercise of warrants | $									$ 2,000,200		$ 1,065,000
Pillar I | Series D Convertible Preferred Stock
Related Party Transactions
Preferred stock, shares issued								1,124,260
Aggregate purchase price under agreement | $								$ 9,500,000
Conversion of preferred stock to common, shares					6,266,175
Pillar I | Common Stock | Series D Warrant
Related Party Transactions
Warrant to purchase common stock								2,810,650
Exercise price of warrants | $ / shares						$ 1.46	$ 1.46	$ 1.63
Pillar I | Common Stock | Series D Warrant | Current Director
Related Party Transactions
Number of people | person								1
Pillar II
Related Party Transactions
Shares issued on exercise of warrants during the period										232,759	1,424,242
Proceeds from exercise of warrants | $										$ 163,000	$ 1,035,000
Pillar II | Series E Convertible Preferred Stock
Related Party Transactions
Preferred stock, shares issued				424,242		424,242	424,242				424,242
Aggregate purchase price under agreement | $						$ 7,000,000
Conversion of preferred stock to common, shares				8,484,840
Pillar II | Common Stock | Series E Warrant
Related Party Transactions
Warrant to purchase common stock						8,484,840	8,484,840
Exercise price of warrants | $ / shares						$ 0.70	$ 0.70
Pillar II | Common Stock | Series E Warrant | Directors
Related Party Transactions
Number of people | person							2
Pillar II | Common Stock | Series E Warrant | Current Director
Related Party Transactions
Number of people | person							1
Pillar II | Common Stock | Series E Warrant | Significant Shareholder
Related Party Transactions
Number of people | person							1
Pillar III
Related Party Transactions
Exercise price of warrants | $ / shares			$ 0.47
Proceeds from equity financings, net of issuance costs | $			$ 2,500,000
Shares issued on exercise of warrants during the period										2,600,000	500,000
Proceeds from exercise of warrants | $										$ 1,222,000	$ 235,000
Pillar III | Common Stock and Matching Warrants Sold
Related Party Transactions
Warrant to purchase common stock			5,000,000
Number of shares of common stock sold in financing			5,000,000
Pillar IV
Related Party Transactions
Number of shares of common stock sold in financing		1,774,193
Proceeds from equity financings, net of issuance costs | $		$ 2,750,000