Stockholders' Equity - September 2018 Financing (Details) $ / shares in Units, $ in Thousands						1 Months Ended				3 Months Ended	12 Months Ended		27 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	Jul. 05, 2016 shares	Mar. 31, 2018 USD ($)	Sep. 30, 2016 USD ($) $ / shares shares	Jul. 31, 2016 USD ($)	Jan. 31, 2016 shares	Jun. 30, 2017 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Sep. 30, 2018 shares	Sep. 24, 2018 USD ($)	Apr. 30, 2018 $ / shares	Apr. 20, 2017 USD ($) $ / shares	Mar. 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
Change in fair value of warrant liability | $											$ (222)	$ 646
Transaction costs | $											$ 690	$ 1,392
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
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
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 Placement Agent Warrants [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Warrant vesting period	6 months
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
September 2018 Warrants, Tranche 2 [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares	2,677,160
Warrant vesting period	6 months
Warrant exercise price (in usd per share)	$ 0.40
September 2018 Warrants, Tranche 1 [Member] | September 2018 Financing [Member]
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares	3,450,000
Warrant vesting period	6 months
Warrant exercise price (in usd per share)	$ 0.30
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
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 1 [Member] | September 2017 Financing [Member]
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares			1,068,307
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]
Shares issuable upon exercise of warrants (in shares) | shares											13,000
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
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
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
Private Placement Warrants [Member] | September 2016 Financing [Member]
Class of Stock [Line Items]
Warrant expiration period							5 years 6 months
February 2015 And January 2016 Warrants [Member]
Class of Stock [Line Items]
Fair value of warrants recorded as equity | $						$ 500
Change in fair value of warrant liability | $						$ 100
Common Stock | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Option Volatility [Member]
Class of Stock [Line Items]
Warrants, measurement input									1.019								0.994
Common Stock | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input									0.016								0.014
Common Stock | Valuation Technique, Option Pricing Model [Member] | Measurement Input, Expected Dividend Rate [Member]
Class of Stock [Line Items]
Warrants, measurement input									0								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
Change in fair value of warrant liability | $										$ 200
Warrants Expiring May 2022
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											82,000
Warrant exercise price (in usd per share)											$ 46.50
Warrants Expiring March 2023, Tranche 2
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											4,000
Warrant exercise price (in usd per share)											$ 21.30
Warrants Expiring January 2023
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											11,000
Warrant exercise price (in usd per share)											$ 12.60
Warrants Expiring March 2023, Tranche 3
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											12,000
Warrant exercise price (in usd per share)											$ 18.90
Warrants Expiring March 2024 Tranche 2
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											115,000
Warrant exercise price (in usd per share)											$ 9.00
Warrants Expiring October 2024
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											1,000
Warrant exercise price (in usd per share)											$ 387.00
Warrants Expiring April 2022
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											8,000
Warrant exercise price (in usd per share)											$ 52.50
Warrants Expiring March 2024 Tranche 3
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											89,000
Warrant exercise price (in usd per share)											$ 12.00
Warrants Expiring July 2025
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											1,000
Warrant exercise price (in usd per share)											$ 492.00
Warrants Expiring May 2023
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											80,000
Warrant exercise price (in usd per share)											$ 15.00
Warrants Expiring March 2024
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											8,000
Warrant exercise price (in usd per share)											$ 10.14
Warrants Expiring January 2023, Tranche 2
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											3,000
Warrant exercise price (in usd per share)											$ 21.30
Warrants Expiring March 2023
Class of Stock [Line Items]
Shares issuable upon exercise of warrants (in shares) | shares											11,000
Warrant exercise price (in usd per share)											$ 12.60
Warrants Cancelled [Member]
Class of Stock [Line Items]
Fair value of warrants recorded as equity | $														$ 600
September 2018 Warrants And Placement Agent Warrants [Member]
Class of Stock [Line Items]
Fair value of warrants recorded as equity | $	$ 900
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
Aspire Capital Fund, LLC [Member]
Class of Stock [Line Items]
Issuance of common stock (in shares) | shares					253,165								500,000
Transaction costs | $								$ 100
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