Stockholders' Equity (Deficit) - Financial Liabilities Subject to Fair Value Measurements (Detail) (Warrants, USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
October 2009 Warrants
Class Of Warrant Or Right [Line Items]
Financial liabilities subject to fair value measurements	$ 1,013	$ 11,320
October 2009 Warrants | Basis of Fair Value Measurements, Level 3
Class Of Warrant Or Right [Line Items]
Financial liabilities subject to fair value measurements	1,013	11,320
March 2011 Warrants
Class Of Warrant Or Right [Line Items]
Financial liabilities subject to fair value measurements	5,551	12,101
March 2011 Warrants | Basis of Fair Value Measurements, Level 3
Class Of Warrant Or Right [Line Items]
Financial liabilities subject to fair value measurements	5,551	12,101
Total Common Stock Warrants
Class Of Warrant Or Right [Line Items]
Financial liabilities subject to fair value measurements	6,564	23,421
Total Common Stock Warrants | Basis of Fair Value Measurements, Level 3
Class Of Warrant Or Right [Line Items]
Financial liabilities subject to fair value measurements	$ 6,564	$ 23,421