Stockholders' Equity - September 2017 Financing (Details) $ / shares in Units, $ in Thousands						1 Months Ended				12 Months Ended		27 Months Ended
	Sep. 20, 2018 USD ($) $ / shares shares	Apr. 02, 2018 USD ($) $ / shares	Sep. 10, 2017 USD ($) $ / shares shares	Apr. 26, 2017 USD ($) $ / shares	Jul. 05, 2016 shares	Sep. 30, 2016 USD ($) $ / shares shares	Jul. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Jan. 31, 2016 USD ($) shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Sep. 30, 2018 shares	Apr. 30, 2018 $ / shares	Apr. 20, 2017 $ / shares
Class of Stock [Line Items]
Aggregate gross proceeds from sale of common stock and warrants | $								$ 7,800	$ 2,200
Transaction costs | $										$ 690	$ 1,392
Amendment of equity classified warrants | $										$ 293	$ 0
September 2018 Financing [Member]
Class of Stock [Line Items]
Net proceeds from sale of common stock and warrants after transaction costs | $	$ 1,100
September 2017 Financing [Member]
Class of Stock [Line Items]
Net proceeds from sale of common stock and warrants after transaction costs | $			$ 3,100
September 2016 Financing [Member]
Class of Stock [Line Items]
Net proceeds from sale of common stock and warrants after transaction costs | $						$ 3,200
Aggregate gross proceeds from sale of common stock and warrants | $						$ 3,700
Common Stock
Class of Stock [Line Items]
Issuance of common stock (in shares) | shares									8,428
Common Stock | September 2018 Financing [Member]
Class of Stock [Line Items]
Issuance of common stock (in shares) | shares	153,333
Shares issued, price per share (in usd per share)	$ 8.10
Transaction costs | $	$ 200
Common Stock | April 2018 Financing [Member]
Class of Stock [Line Items]
Transaction costs | $		$ 700
Common Stock | September 2017 Financing [Member]
Class of Stock [Line Items]
Issuance of common stock (in shares) | shares			2,136,614
Shares issued, price per share (in usd per share)			$ 1.73
Aggregate gross proceeds from sale of common stock and warrants | $			$ 2,800
Transaction costs | $			$ 600
Common Stock | April 2017 Financing [Member]
Class of Stock [Line Items]
Transaction costs | $				$ 1,100
Common Stock | September 2016 Financing [Member]
Class of Stock [Line Items]
Issuance of common stock (in shares) | shares						1,082,402
Shares issued, price per share (in usd per share)						$ 3.45
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, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input	0
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 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, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input	0
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
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, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input		0
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 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, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input		0
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
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
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] | Warrants Not Settleable in Cash [Member] | September 2017 Financing [Member]
Class of Stock [Line Items]
Aggregate gross proceeds from sale of common stock and warrants | $			$ 900
Warrants Expiring March 2020, Tranche 1 [Member] | September 2017 Financing [Member]
Class of Stock [Line Items]
Date from which warrants are exercisable			Sep. 13, 2017
Warrant exercise price (in usd per share)			$ 1.67										$ 0.60
Warrant expiration period			2 years 6 months
Warrants Expiring March 2020, Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										$ 18.00
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
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
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
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, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input								0	0
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
Warrants Expiring July 2025
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										492.00
Warrants Expiring May 2023
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										15.00
Warrants Expiring March 2023
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										12.60
Warrants Expiring January 2023, Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										21.30
Warrants Expiring May 2022
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										46.50
Warrants Expiring March 2024
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										10.14
Warrants Expiring March 2023, Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										21.30
Warrants Expiring January 2023
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										12.60
Warrants Expiring April 2022
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										52.50
Warrants Expiring March 2024 Tranche 3
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										12.00
Warrants Expiring March 2023, Tranche 3
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										18.90
Warrants Expiring October 2024
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										387.00
Warrants Expiring March 2024 Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)										$ 9.00
September 2018 Warrants, Tranche 1 [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)	$ 0.30
September 2018 Warrants, Tranche 2 [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Warrant exercise price (in usd per share)	$ 0.40
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
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
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
Aspire Capital Fund, LLC [Member]
Class of Stock [Line Items]
Issuance of common stock (in shares) | shares					253,165							500,000
Transaction costs | $							$ 100