Stockholders' Equity - September 2016 Financing (Details) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended				3 Months Ended		12 Months Ended
	Sep. 20, 2018	Apr. 02, 2018	Sep. 10, 2017	Apr. 26, 2017	Mar. 31, 2018	Sep. 30, 2016	Mar. 31, 2016	Jan. 31, 2016	Jun. 30, 2017	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Sep. 24, 2018	Apr. 30, 2018	Apr. 20, 2017
Stockholders Equity Note [Line Items]
Aggregate gross proceeds from sale of common stock and warrants							$ 7,800	$ 2,200
Shares issuable upon exercise of warrants (in shares)											437,000
Other financing costs										$ 400
Transaction costs											$ 690	$ 1,392
Fair value of warrants recorded as equity															$ 800
Change in fair value of warrant liability											$ (222)	$ 646
September 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Net proceeds from sale of common stock and warrants after transaction costs	$ 1,100
September 2017 Financing [Member]
Stockholders Equity Note [Line Items]
Net proceeds from sale of common stock and warrants after transaction costs			$ 3,100
September 2016 Financing [Member]
Stockholders Equity Note [Line Items]
Aggregate gross proceeds from sale of common stock and warrants						$ 3,700
Net proceeds from sale of common stock and warrants after transaction costs						$ 3,200
Common Stock
Stockholders Equity Note [Line Items]
Issuance of common stock (in shares)								8,428
Common Stock | September 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Issuance of common stock (in shares)	153,333
Shares issued, price per share (in usd per share)	$ 8.10
Transaction costs	$ 200
Common Stock | April 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Transaction costs		$ 700
Common Stock | September 2017 Financing [Member]
Stockholders Equity Note [Line Items]
Issuance of common stock (in 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]
Stockholders Equity Note [Line Items]
Number of securities called by each warrant (in shares)				0.75
Transaction costs				$ 1,100
Common Stock | September 2016 Financing [Member]
Stockholders Equity Note [Line Items]
Issuance of common stock (in shares)						1,082,402
Shares issued, price per share (in usd per share)						$ 3.45				$ 3.45
Transaction costs						$ 400
September 2018 Warrants [Member] | September 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Warrant expiration period	5 years
September 2018 Placement Agent Warrants [Member] | September 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)	$ 0.3375
Warrant expiration period	5 years
April 2018 Warrants [Member] | April 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Number of securities called by each warrant (in shares)		0.5
Exercise price (in usd per share)		$ 0.50
Warrant expiration period		5 years
April 2018 Placement Agent Warrants [Member] | April 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)		$ 0.625
Warrant expiration period		5 years
Warrants Expiring March 2020, Tranche 2
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 18.00
Shares issuable upon exercise of warrants (in shares)											13,000
Warrants Expiring March 2020, Tranche 2 | September 2017 Financing [Member]
Stockholders Equity Note [Line Items]
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]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)			$ 1.67											$ 0.60
Shares issuable upon exercise of warrants (in shares)			1,068,307
Warrant expiration period			2 years 6 months
Underwriter Warrants 2017 [Member] | April 2017 Financing [Member]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)				$ 1.75
Warrant expiration period				5 years
April 2017 Warrants [Member] | April 2017 Financing [Member]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)				$ 1.55
Warrant expiration period				5 years
Private Placement Warrants [Member] | September 2016 Financing [Member]
Stockholders Equity Note [Line Items]
Warrants, period in which warrants exercisable						6 months
Warrant expiration period						5 years 6 months
Placement Agent Warrants [Member] | September 2016 Financing [Member]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)						$ 4.3125				$ 4.3125
Warrant expiration period						5 years
Proceeds from issuance private placement warrants						$ 1,600
Payment of transaction costs						500
Non-cash transaction costs						100
Other financing costs						$ 300
February 2015 And January 2016 Warrants [Member]
Stockholders Equity Note [Line Items]
Fair value of warrants recorded as equity					$ 500
Change in fair value of warrant liability					$ 100
Common Stock
Stockholders Equity Note [Line Items]
Other financing costs							$ 200
Private Placement And Placement Agent Warrants [Member] | April 2017 Warrant Amendment [Member]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)															$ 1.55
Change in fair value of warrant liability									$ 200
Warrants Expiring January 2023, Tranche 2
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 21.30
Shares issuable upon exercise of warrants (in shares)											3,000
Warrants Expiring March 2023
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 12.60
Shares issuable upon exercise of warrants (in shares)											11,000
Warrants Expiring May 2023
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 15.00
Shares issuable upon exercise of warrants (in shares)											80,000
Warrants Expiring May 2022
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 46.50
Shares issuable upon exercise of warrants (in shares)											82,000
Warrants Expiring March 2023, Tranche 2
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 21.30
Shares issuable upon exercise of warrants (in shares)											4,000
Warrants Expiring January 2023
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 12.60
Shares issuable upon exercise of warrants (in shares)											11,000
Warrants Expiring July 2025
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 492.00
Shares issuable upon exercise of warrants (in shares)											1,000
Warrants Expiring March 2024 Tranche 3
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 12.00
Shares issuable upon exercise of warrants (in shares)											89,000
Warrants Expiring March 2023, Tranche 3
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 18.90
Shares issuable upon exercise of warrants (in shares)											12,000
Warrants Expiring March 2024 Tranche 2
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 9.00
Shares issuable upon exercise of warrants (in shares)											115,000
Warrants Expiring April 2022
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 52.50
Shares issuable upon exercise of warrants (in shares)											8,000
Warrants Expiring October 2024
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 387.00
Shares issuable upon exercise of warrants (in shares)											1,000
Warrants Expiring March 2024
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)											$ 10.14
Shares issuable upon exercise of warrants (in shares)											8,000
Warrants Cancelled [Member]
Stockholders Equity Note [Line Items]
Fair value of warrants recorded as equity													$ 600
September 2018 Warrants And Placement Agent Warrants [Member]
Stockholders Equity Note [Line Items]
Fair value of warrants recorded as equity	$ 900
September 2018 Warrants, Tranche 1 [Member] | September 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)	$ 0.30
Shares issuable upon exercise of warrants (in shares)	3,450,000
September 2018 Warrants, Tranche 2 [Member] | September 2018 Financing [Member]
Stockholders Equity Note [Line Items]
Exercise price (in usd per share)	$ 0.40
Shares issuable upon exercise of warrants (in shares)	2,677,160
April 2018 Warrants And Placement Agent Warrants [Member]
Stockholders Equity Note [Line Items]
Fair value of warrants recorded as equity		$ 1,200