Equity - Common Stock (Details) $ / shares in Units, $ in Thousands											6 Months Ended
	Dec. 11, 2018 USD ($) shares	Jul. 05, 2018 USD ($) $ / shares shares	Jul. 02, 2018 $ / shares shares	May 31, 2018 USD ($) $ / shares	May 29, 2018 $ / shares shares	May 24, 2018 $ / shares	Jan. 06, 2018 $ / shares shares	Dec. 11, 2017 USD ($)	Dec. 08, 2017 $ / shares shares	Dec. 07, 2017 $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 $ / shares shares	Mar. 31, 2018 shares	Dec. 31, 2017 shares	Jul. 31, 2016 shares	Jun. 30, 2016 shares
Class of Stock [Line Items]
Common stock, shares authorized (shares) | shares											150,000,000		150,000,000			150,000,000	100,000,000
Stock split, conversion ratio						0.2
Common stock, par value (in dollars per share)			$ 0.001			$ 0.001					$ 0.001		$ 0.001
Sale of common stock (shares) | shares							409,091
Number of warrants (shares) | shares											7,392,966		7,392,966
Common stock purchased with warrant (shares) | shares										1
Warrant exercise price (in dollars per share)											$ 7.36		$ 7.36
Period to exercise options										30 days
Purchase price (in usd per share)							$ 3.80
Proceeds from common stock offering, net | $				$ 5,300				$ 9,300			$ 0	$ 5,473
Percentage of aggregate shares of common stock available for purchase				7.00%
Issued in December 2017 Offering - pre-funded warrants
Class of Stock [Line Items]
Number of warrants (shares) | shares										1,184,442				1,184,442	1,184,442
Issued in December 2017 Offering - common warrants
Class of Stock [Line Items]
Number of warrants (shares) | shares							409,091		82,118	2,727,273					82,118
Purchase price (in usd per share)							$ 0.01
Public Stock Offering
Class of Stock [Line Items]
Sale of common stock (shares) | shares										1,542,832
May 2018 Purchase Agreement
Class of Stock [Line Items]
Common stock, par value (in dollars per share)					$ 0.001
Sale of common stock (shares) | shares					2,038,224
Purchase price (in usd per share)					$ 2.85
Percentage of shares of common stock sold					75.00%
July 2018 Purchase Agreement
Class of Stock [Line Items]
Common stock, par value (in dollars per share)			$ 2.69
Sale of common stock (shares) | shares			1,474,080
Proceeds from common stock offering, net | $		$ 3,600
Percentage of shares of common stock sold			65.00%
Warrant | Issued in December 2017 Offering - pre-funded warrants
Class of Stock [Line Items]
Warrant exercise price (in dollars per share)											$ 0.05
Warrant | Issued in December 2017 Offering - common warrants
Class of Stock [Line Items]
Warrant exercise price (in dollars per share)							$ 3.85			$ 3.85	$ 3.85
Warrant exercise period											5 years
Warrant | Issued in December 2017 Offering - underwriter warrants
Class of Stock [Line Items]
Number of warrants (shares) | shares									87,274
Warrant exercise price (in dollars per share)									$ 4.8125
Warrant exercise period									5 years
Warrant | Issued in May 2018 Private Placement - common warrants
Class of Stock [Line Items]
Number of warrants (shares) | shares					1,528,668
Warrant exercise price (in dollars per share)					$ 2.86
Purchase price (in usd per share)					$ 0.125
Warrant exercise period					5 years 6 months
Warrant | Issued in July 2018 - underwriter warrants
Class of Stock [Line Items]
Warrant exercise price (in dollars per share)				$ 3.679
Warrant exercise period				5 years
Warrant | Warrants Issued in July 2018 Private Placement
Class of Stock [Line Items]
Number of warrants (shares) | shares			958,152
Warrant exercise price (in dollars per share)		$ 3.464	$ 2.70
Purchase price (in usd per share)			$ 0.125
Warrant exercise period		5 years	5 years 6 months
Warrants to purchase shares of common stock (in shares) | shares		103,186
Common Stock | December 2018 Private Placement
Class of Stock [Line Items]
Sale of common stock (shares) | shares	443,350
Consideration received, gross | $	$ 900
Consideration received, net | $	$ 800