Stockholders' Equity - June and March 2018 Warrant Amendments (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Sep. 24, 2018	Sep. 20, 2018	Apr. 02, 2018	Apr. 20, 2017
Class of Stock [Line Items]
Amendment of equity classified warrants		$ 293	$ 0
Fair value of warrants recorded as equity							$ 800
Change in fair value of warrant liability		$ (222)	$ 646
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
Warrants Expiring May 2022
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		$ 46.50
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 March 2024
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		10.14
Warrants Expiring January 2023, Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		21.30
Warrants Expiring March 2023
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		12.60
Warrants Expiring May 2023
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		15.00
Warrants Expiring July 2025
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		492.00
Warrants Expiring March 2024 Tranche 3
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		12.00
Warrants Expiring April 2022
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		52.50
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
Warrants Expiring March 2020, Tranche 2
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		18.00
Warrants Expiring March 2023, Tranche 3
Class of Stock [Line Items]
Warrant exercise price (in usd per share)		$ 18.90
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