Stockholders' Equity - Equity Offerings (Details) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended	12 Months Ended
	Dec. 16, 2016	Nov. 04, 2016	Nov. 23, 2015	Jun. 02, 2015	Dec. 16, 2016	Dec. 31, 2016	Dec. 31, 2015
Subsidiary, Sale of Stock [Line Items]
Proceeds from equity offerings, net of costs						$ 10,200	$ 7,115
June 2015 Offering
Subsidiary, Sale of Stock [Line Items]
Units offered for sale				500,000
Unit price (in dollars per share)				$ 10.25
Number of shares of stock into which each warrant may be converted (in shares)				1
Share component per unit sold (in shares)				1
Net proceeds allocated to equity				$ 3,700
November 2015 Offering
Subsidiary, Sale of Stock [Line Items]
Shares issued			176,772
Share price (in dollars per share)			$ 6.10
Gross proceeds allocated to equity			$ 100
November 2016 Offering
Subsidiary, Sale of Stock [Line Items]
Net proceeds allocated to warrant liability	$ 900
Warrants Issued June 2015, Liability
Subsidiary, Sale of Stock [Line Items]
Exercise period				5 years 6 months
Warrants Issued June 2015, Liability | June 2015 Offering
Subsidiary, Sale of Stock [Line Items]
Warrant component per unit sold (in shares)				0.2
Exercise price (in dollars per share)				$ 13.25
Expiration period				6 months
Proceeds from issuance of common stock and warrants				$ 5,100
Proceeds from equity offerings, net of costs				$ 4,500
Net proceeds allocated to warrant liability						800
Additional underwriting discounts and commissions and offering costs allocated to warrants						$ 100
Series B Warrants | November 2015 Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares of stock into which each warrant may be converted (in shares)			1
Exercise price (in dollars per share)			$ 0.05
Number of shares into which warrants may be converted (in shares)			337,228
Warrant price (in dollars per share)			$ 6.05
Exercise period			2 years
Series A Warrants | November 2015 Offering
Subsidiary, Sale of Stock [Line Items]
Exercise price (in dollars per share)			$ 8.50
Expiration period			7 years
Number of shares into which warrants may be converted (in shares)			154,200
Exercise period			5 years
Warrant issued for purchase of one common stock purchased through pre-funded warrants			0.3
Warrants Issued November 2015, Liability | November 2015 Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares of stock into which each warrant may be converted (in shares)			1
Proceeds from equity offerings, net of costs			$ 2,600
Additional underwriting discounts and commissions and offering costs allocated to warrants							$ 400
Number of shares into which surrendered and cancelled warrants could have been converted			171,279
Exercise price of warrants surrendered and cancelled (in dollars per share)			$ 15.95
Gross proceeds from equity offerings			$ 3,100
Gross proceeds allocated to warrant liability			3,400
Offering costs allocated to warrants issued			$ 400
Series C-1, Series C-2 and Series C-3 Warrants | November 2015 Offering
Subsidiary, Sale of Stock [Line Items]
Exercise price (in dollars per share)			$ 8.50
Expiration period			7 years
Number of shares into which warrants may be converted (in shares)			171,279
Expiration period			7 months
Common Stock
Subsidiary, Sale of Stock [Line Items]
Shares issued						5,662,000	677,000
Issuance of stock for settlement of accounts payable (in shares)						81,000
Common Stock | November 2016 Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares of stock into which each warrant may be converted (in shares)	489,475				489,475
Exercise price (in dollars per share)	$ 2.20				$ 2.20
Proceeds from equity offerings, net of costs					$ 10,200
Net proceeds allocated to equity					$ 9,300
Additional underwriting discounts and commissions and offering costs allocated to warrants	$ 100
Shares issued	4,222,290	949,960			5,172,250
Share price (in dollars per share)	$ 2.00				$ 2.00
Gross proceeds from equity offerings	$ 8,400	$ 1,900			$ 10,300
Issuance of stock for settlement of accounts payable (in shares)					489,475