Warrants to Acquire Shares of Common Stock (Fair Value of Warrants is Estimated Using Black-Scholes Option Pricing Model) (Details) - $ / shares shares in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	1,812	963
Series A Convertible Preferred
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	1,384	0
Strike price (in usd per share)	$ 6.59
Expected term (years)	5 years 3 months 7 days
Volatility %	83.70%
Risk-free rate %	2.74%
Galena February 2017
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	32	567
Strike price (in usd per share)	$ 33.00	$ 13.00
Expected term (years)	3 years 7 months 17 days	4 years 1 month 13 days
Volatility %	82.74%	79.29%
Risk-free rate %	2.25%	2.09%
Galena Other
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	80	80
Strike price (in usd per share)	$ 888.22	$ 28.40
Expected term (years)	2 years 8 months 9 days	3 years 2 months 9 days
Volatility %	83.06%	74.05%
Risk-free rate %	2.32%	2.09%