Warrants to Acquire Shares of Common Stock (Changes in Fair Value of Warrant Liability) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Class of Warrant or Right, Fair Value [Roll Forward]
Warrant liability, Beginning balance	$ 1,309
Fair value of warrants granted	5,039
Fair value of warrants canceled	(524)
Change in fair value of warrants	(3,099)
Warrant liability, Ending balance	2,725
Series A Convertible Preferred
Class of Warrant or Right, Fair Value [Roll Forward]
Warrant liability, Beginning balance	0
Fair value of warrants granted	5,039
Fair value of warrants canceled	0
Change in fair value of warrants	(2,331)
Warrant liability, Ending balance	2,708
Galena February 2017
Class of Warrant or Right, Fair Value [Roll Forward]
Warrant liability, Beginning balance	1,305
Fair value of warrants granted	0
Fair value of warrants canceled	(524)
Change in fair value of warrants	(764)
Warrant liability, Ending balance	17
Galena Other
Class of Warrant or Right, Fair Value [Roll Forward]
Warrant liability, Beginning balance	4
Fair value of warrants granted	0
Fair value of warrants canceled	0
Change in fair value of warrants	(4)
Warrant liability, Ending balance	$ 0