Equity - Common Stock (Details) $ / shares in Units, $ in Thousands												1 Months Ended		12 Months Ended
	Dec. 11, 2018 USD ($) shares	Jul. 05, 2018 USD ($) $ / shares shares	Jul. 02, 2018 $ / shares shares	May 31, 2018 USD ($) $ / shares shares	May 29, 2018 $ / shares shares	May 24, 2018 $ / shares	Jan. 06, 2018 $ / shares shares	Dec. 11, 2017 USD ($) $ / shares	Dec. 08, 2017 $ / shares shares	Dec. 07, 2017 $ / shares shares	Mar. 10, 2017 $ / shares	May 31, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Jul. 31, 2016 shares
Class of Stock [Line Items]
Common stock, shares authorized (in shares)													150,000,000	150,000,000	150,000,000	100,000,000
Reverse stock split (percentage)						0.2					0.3333
Common stock, par value (in dollars per share) | $ / shares			$ 0.001			$ 0.001					$ 0.001		$ 0.001	$ 0.001	$ 0.001
Sale of common stock (shares)							409,091
Number of warrants (shares)													5,452,923	7,392,966	5,452,923
Purchase price (in usd per share) | $ / shares							$ 3.80
Warrants exercise price (usd per share) | $ / shares													$ 11.32	$ 7.36	$ 11.32
Proceeds from common stock offerings, (net of offering costs of $1,170) | $				$ 5,300				$ 9,300						$ 8,915	$ 9,749
Percentage of aggregate shares of common stock available for purchase				7.00%
Issued in 2017 Common Stock Offering - pre-funded warrants
Class of Stock [Line Items]
Number of warrants (shares)										1,184,422			1,184,422		1,184,422
Issued in 2017 Common Stock Offering - common warrants
Class of Stock [Line Items]
Number of warrants (shares)							409,091		82,118	2,809,404			82,118		82,118
Purchase price (in usd per share) | $ / shares							$ 0.05
Warrants
Class of Stock [Line Items]
Number of warrants (shares)													4,067,367	6,187,126	4,067,367
Warrants | Warrants Issued in July 2018 Private Placement
Class of Stock [Line Items]
Number of warrants (shares)			958,152
Purchase price (in usd per share) | $ / shares			$ 0.125
Warrants exercise price (usd per share) | $ / shares		$ 3.464	$ 2.70
Warrant exercise period		5 years	5 years 6 months
Shares of common stock available for purchase		103,186
Warrants | Warrants Issued in 2018 Private Placement - Common Warrants
Class of Stock [Line Items]
Number of warrants (shares)				1,528,668								1,528,668
Purchase price (in usd per share) | $ / shares					$ 0.125
Warrants exercise price (usd per share) | $ / shares				$ 2.86								$ 2.86
Warrant exercise period					5 years 6 months							5 years 6 months
Warrants | Issued in May 2018 Registered Direct Offering - underwriter warrants
Class of Stock [Line Items]
Number of warrants (shares)				142,676								142,676	0	142,676	0
Warrants exercise price (usd per share) | $ / shares				$ 3.679								$ 3.679		$ 3.679
Warrant exercise period				5 years
Warrants | Issued in 2017 Common Stock Offering - pre-funded warrants
Class of Stock [Line Items]
Number of warrants (shares)													483,221	0	483,221
Warrants exercise price (usd per share) | $ / shares								$ 0.05						$ 0.05
Warrants | Issued in 2017 Common Stock Offering - common warrants
Class of Stock [Line Items]
Number of warrants (shares)													2,809,404	2,679,702	2,809,404
Warrants exercise price (usd per share) | $ / shares							$ 3.85	$ 3.85		$ 3.85			$ 3.85	$ 3.85	$ 3.85
Warrant exercise period								5 years					5 years
Warrants | Issued in 2017 Common Stock Offering - underwriter warrants
Class of Stock [Line Items]
Number of warrants (shares)									87,274				87,274	87,274	87,274
Warrants exercise price (usd per share) | $ / shares								$ 4.8125	$ 4.8125				$ 4.8125	$ 4.8125	$ 4.8125
Warrant exercise period								5 years	5 years				5 years
July 2018 Purchase Agreement
Class of Stock [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 2.69
Sale of common stock (shares)			1,474,080
Percentage of common stock sold			65.00%
Proceeds from common stock offerings, (net of offering costs of $1,170) | $		$ 3,600
May 2018 Purchase Agreement
Class of Stock [Line Items]
Common stock, par value (in dollars per share) | $ / shares					$ 0.001
Sale of common stock (shares)					2,038,224
Percentage of common stock sold					75.00%
Purchase price (in usd per share) | $ / shares					$ 2.85
Public Stock Offering
Class of Stock [Line Items]
Sale of common stock (shares)										1,542,832
Common Stock | Issued in 2017 Common Stock Offering - common warrants
Class of Stock [Line Items]
Number of shares per warrant (shares)										1
Common Stock | Warrants | Issued in 2017 Common Stock Offering - common warrants
Class of Stock [Line Items]
Number of shares per warrant (shares)													1		1
Common Stock | December 2018 Private Placement
Class of Stock [Line Items]
Sale of common stock (shares)	443,350
Gross consideration received for sale of stock | $	$ 900
Expected proceeds from offering | $	$ 800