Equity - Common Stock (Details) $ / shares in Units, $ in Thousands							6 Months Ended		12 Months Ended
	May 31, 2018 USD ($) $ / shares shares	May 29, 2018 $ / shares shares	Jan. 06, 2018 $ / shares shares	Dec. 11, 2017 USD ($)	Dec. 07, 2017 $ / shares shares	Mar. 10, 2017	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($)	Dec. 31, 2017 $ / shares shares	May 24, 2018 $ / shares	Dec. 08, 2017 shares	Jul. 31, 2016 shares
Class of Stock [Line Items]
Common stock, shares authorized (shares)							150,000,000		150,000,000
Stock split, conversion ratio						0.3333
Common stock, par value (in dollars per share) | $ / shares							$ 0.001		$ 0.001	$ 0.001
Sale of common stock (shares)			409,091
Number of warrants (shares)							6,436,304		5,452,923
Common stock purchased with warrant (shares)					1
Purchase price (in usd per share) | $ / shares			$ 3.80
Warrant exercise price (in dollars per share) | $ / shares							$ 9.83		$ 11.32
Proceeds from common stock offering, net | $	$ 5,400			$ 9,300			$ 5,473	$ 0
Percentage of aggregate shares of common stock available for purchase	7.00%
Minimum
Class of Stock [Line Items]
Common stock, shares authorized (shares)												100,000,000
Maximum
Class of Stock [Line Items]
Common stock, shares authorized (shares)												150,000,000
Issued in December 2017 Offering - pre-funded warrants
Class of Stock [Line Items]
Number of warrants (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)			409,091		2,727,273						82,118
Purchase price (in usd per share) | $ / shares			$ 0.01
Warrant
Class of Stock [Line Items]
Number of warrants (shares)							5,125,788		4,067,367
Warrant | Issued in December 2017 Offering - pre-funded warrants
Class of Stock [Line Items]
Number of warrants (shares)							0		483,221
Warrant exercise price (in dollars per share) | $ / shares							$ 0.05
Warrant | Issued in December 2017 Offering - common warrants
Class of Stock [Line Items]
Number of warrants (shares)							2,679,702		2,809,404
Warrant exercise price (in dollars per share) | $ / shares			$ 3.85		$ 3.85		$ 3.85		$ 3.85
Warrant exercise period							5 years		5 years
Warrant | Issued in December 2017 Offering - underwriter warrants
Class of Stock [Line Items]
Number of warrants (shares)							87,274		87,274
Warrant exercise price (in dollars per share) | $ / shares							$ 4.8125		$ 4.8125
Warrant exercise period							5 years		5 years
Warrant | Issued in May 2018 Private Placement - common warrants
Class of Stock [Line Items]
Number of warrants (shares)	1,528,668						1,528,668		0
Purchase price (in usd per share) | $ / shares		$ 0.125
Warrant exercise price (in dollars per share) | $ / shares	$ 2.86						$ 2.86
Warrant exercise period		5 years 6 months
Warrant | Issued in May 2018 - underwriter warrants
Class of Stock [Line Items]
Number of warrants (shares)	142,676						142,676		0
Warrant exercise price (in dollars per share) | $ / shares	$ 3.679						$ 3.679
Warrant exercise period	5 years
Public Stock Offering
Class of Stock [Line Items]
Sale of common stock (shares)					1,542,832
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 shares of common stock sold		75.00%
Purchase price (in usd per share) | $ / shares		$ 2.85