Warrants - Fair Value of Warrants is Estimated Using Black-Scholes Option Pricing Model (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Class of Warrant or Right [Line Items]
Warrants outstanding	963	0
Galena February 2017
Class of Warrant or Right [Line Items]
Warrants outstanding	567	0
Strike price (per share)	$ 33.00
Expected term (years)	4 years 1 month 13 days
Volatility%	79.29%
Risk-free rate %	2.09%
Other Galena Warrant Issues Accounted for as Liabilities [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding	76
Strike price (per share)	$ 888.22
Expected term (years)	2 years 8 months 26 days
Volatility%	72.46%
Risk-free rate %	2.00%