Stockholders' Equity - April 2018 Financing & Warrant Amendment (Details) $ / shares in Units, $ in Thousands					1 Months Ended		12 Months Ended
	Sep. 20, 2018 USD ($) $ / shares shares	Apr. 02, 2018 USD ($) $ / shares shares	Sep. 10, 2017 USD ($) $ / shares shares	Apr. 26, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares	Jul. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Sep. 24, 2018 USD ($)	Apr. 30, 2018 $ / shares	Mar. 31, 2018 USD ($)	Apr. 20, 2017 USD ($) $ / shares	Mar. 31, 2016	Jan. 31, 2016
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares							437,000
Fair value of warrants recorded as equity | $												$ 800
Transaction costs | $							$ 690	$ 1,392
Common Stock | September 2018 Financing [Member]
Class of Stock [Line Items]
Transaction costs | $	$ 200
Common Stock | April 2018 Financing [Member]
Class of Stock [Line Items]
Net proceeds from financing transaction | $		$ 2,900
Number of units sold in transaction (in shares) | shares		7,100,000
Transaction costs | $		$ 700
Common Stock | September 2017 Financing [Member]
Class of Stock [Line Items]
Transaction costs | $			$ 600
Common Stock | April 2017 Financing [Member]
Class of Stock [Line Items]
Net proceeds from financing transaction | $				$ 5,900
Transaction costs | $				$ 1,100
Common Stock | September 2016 Financing [Member]
Class of Stock [Line Items]
Transaction costs | $					$ 400
September 2018 Warrants [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Warrant expiration period	5 years
September 2018 Warrants [Member] | September 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input	1.073
September 2018 Warrants [Member] | September 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input	0.0297
September 2018 Warrants [Member] | September 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input	0
September 2018 Placement Agent Warrants [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)	$ 0.3375
Warrant expiration period	5 years
September 2018 Placement Agent Warrants [Member] | September 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input	1.073
September 2018 Placement Agent Warrants [Member] | September 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input	0.0297
September 2018 Placement Agent Warrants [Member] | September 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input	0
April 2018 Placement Agent Warrants [Member] | April 2018 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		$ 0.625
Warrant expiration period		5 years
April 2018 Placement Agent Warrants [Member] | April 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input		1.05
April 2018 Placement Agent Warrants [Member] | April 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input		0.0255
April 2018 Placement Agent Warrants [Member] | April 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input		0
April 2018 Warrants [Member] | April 2018 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		$ 0.50
Warrant expiration period		5 years
April 2018 Warrants [Member] | April 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input		1.040
April 2018 Warrants [Member] | April 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input		0.0255
April 2018 Warrants [Member] | April 2018 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input		0
September 2017 Financing Warrants [Member] | September 2017 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input			1.104
September 2017 Financing Warrants [Member] | September 2017 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input			0.0138
September 2017 Financing Warrants [Member] | September 2017 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input			0
Warrants Expiring March 2020, Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 18.00
Shares issuable upon exercise of warrants (in shares) | shares							13,000
Warrants Expiring March 2020, Tranche 2 | September 2017 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)			$ 2.16							$ 0.60
Warrant expiration period			2 years 6 months
Warrants Expiring March 2020, Tranche 1 [Member] | September 2017 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)			$ 1.67							$ 0.60
Warrant expiration period			2 years 6 months
Shares issuable upon exercise of warrants (in shares) | shares			1,068,307
Underwriter Warrants 2017 [Member] | April 2017 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)				$ 1.75
Warrant expiration period				5 years
Underwriter Warrants 2017 [Member] | April 2017 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input				0.887
April 2017 Warrants [Member] | April 2017 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)				$ 1.55
Warrant expiration period				5 years
April 2017 Warrants [Member] | April 2017 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input				0.883
Private Placement Warrants [Member] | September 2016 Financing [Member]
Class of Stock [Line Items]
Warrant expiration period					5 years 6 months
Placement Agent Warrants [Member] | September 2016 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)					$ 4.3125
Warrant expiration period					5 years
Common Stock | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input													0.994	1.019
Common Stock | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input													0.014	0.016
Common Stock | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input													0	0
Warrants Expiring May 2022
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 46.50
Shares issuable upon exercise of warrants (in shares) | shares							82,000
Warrants Expiring March 2023, Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 21.30
Shares issuable upon exercise of warrants (in shares) | shares							4,000
Warrants Expiring January 2023
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 12.60
Shares issuable upon exercise of warrants (in shares) | shares							11,000
Warrants Expiring March 2023, Tranche 3
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 18.90
Shares issuable upon exercise of warrants (in shares) | shares							12,000
Warrants Expiring March 2024 Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 9.00
Shares issuable upon exercise of warrants (in shares) | shares							115,000
Warrants Expiring October 2024
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 387.00
Shares issuable upon exercise of warrants (in shares) | shares							1,000
Warrants Expiring April 2022
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 52.50
Shares issuable upon exercise of warrants (in shares) | shares							8,000
Warrants Expiring March 2024 Tranche 3
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 12.00
Shares issuable upon exercise of warrants (in shares) | shares							89,000
Warrants Expiring July 2025
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 492.00
Shares issuable upon exercise of warrants (in shares) | shares							1,000
Warrants Expiring May 2023
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 15.00
Shares issuable upon exercise of warrants (in shares) | shares							80,000
Warrants Expiring March 2023
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 12.60
Shares issuable upon exercise of warrants (in shares) | shares							11,000
Warrants Expiring January 2023, Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 21.30
Shares issuable upon exercise of warrants (in shares) | shares							3,000
Warrants Expiring March 2024
Class of Stock [Line Items]
Warrant exercise price (in usd per share)							$ 10.14
Shares issuable upon exercise of warrants (in shares) | shares							8,000
Warrants Cancelled [Member]
Class of Stock [Line Items]
Fair value of warrants recorded as equity | $									$ 600
September 2018 Warrants, Tranche 1 [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)	$ 0.30
Shares issuable upon exercise of warrants (in shares) | shares	3,450,000
September 2018 Warrants, Tranche 2 [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)	$ 0.40
Shares issuable upon exercise of warrants (in shares) | shares	2,677,160
September 2018 Warrants And Placement Agent Warrants [Member]
Class of Stock [Line Items]
Fair value of warrants recorded as equity | $	$ 900
February 2015 And January 2016 Warrants [Member]
Class of Stock [Line Items]
Fair value of warrants recorded as equity | $											$ 500
April 2018 Warrants And Placement Agent Warrants [Member]
Class of Stock [Line Items]
Fair value of warrants recorded as equity | $		$ 1,200
April 2017 Financing Warrants [Member] | April 2017 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input				0.018
April 2017 Financing Warrants [Member] | April 2017 Financing [Member] | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input				0
Private Placement And Placement Agent Warrants [Member] | April 2017 Warrant Amendment [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)												$ 1.55
HC Wainwright [Member] | Common Stock | April 2017 Financing [Member]
Class of Stock [Line Items]
Number of units sold in transaction (in shares) | shares				5,030,000
HC Wainwright [Member] | September 2018 Placement Agent Warrants [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares	230,000
HC Wainwright [Member] | April 2018 Placement Agent Warrants [Member] | April 2018 Financing [Member]
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares		355,000
HC Wainwright [Member] | Warrants Expiring March 2020, Tranche 2 | September 2017 Financing [Member]
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares			106,831
HC Wainwright [Member] | Underwriter Warrants 2017 [Member] | April 2017 Financing [Member]
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares				251,500
Aspire Capital Fund, LLC [Member]
Class of Stock [Line Items]
Transaction costs | $						$ 100