Debt and Fair Value of Financial Instruments - Aggregate Fair Value and Carrying Value of Warrant Liability and Short and Long-term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Warrant liability	$ 9,918
Short-term debt, related party		$ 1,000
Long-term debt, related party	1,200	1,200
Long-term debt	1,755	1,558
Total	12,873	3,758
Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Warrant liability	9,918
Short-term debt, related party		1,000
Long-term debt, related party	1,200	1,200
Long-term debt	1,755	1,558
Total	$ 12,873	$ 3,758