Liquidity, Uncertainties and Going Concern - Additional Information (Detail) - USD ($)	Jan. 07, 2018	Jan. 26, 2018	Dec. 31, 2017	Sep. 20, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit			$ 473,921,000		$ 424,239,000
Cash and cash equivalents			25,961,000		$ 9,866,000	$ 2,789,000
Restricted cash			$ 500,000
Minimum
Class of Stock [Line Items]
Share price (usd per share)				$ 1.00
Aspire Capital | Purchase Agreement
Class of Stock [Line Items]
Common stock purchase agreement (up to)				$ 20,000,000
Aspire Capital | Subsequent Event
Class of Stock [Line Items]
Shares limited to purchase (shares)	1,375,868
Shares limited to purchase, percent	19.99%
Commitment fee for Purchase Agreement, shares	125,000
Aspire Capital | Subsequent Event | Minimum
Class of Stock [Line Items]
Average price paid (usd per share)	$ 3.02
Share price (usd per share)	$ 1.0
Aspire Capital | Subsequent Event | Purchase Agreement
Class of Stock [Line Items]
Common stock purchase agreement (up to)	$ 20,000,000
FBR | Subsequent Event | ATM Agreement
Class of Stock [Line Items]
Common stock purchase agreement (up to)		$ 2,800,000.0