Stockholders' Equity (Deficit) - Financial Liabilities Subject to Fair Value Measurements (Detail) (Warrants, USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Inputs Liabilities Quantitative Information [Line Items]
Financial liabilities subject to fair value measurements		$ 23,421
Basis of Fair Value Measurements, Level 3
Fair Value Inputs Liabilities Quantitative Information [Line Items]
Financial liabilities subject to fair value measurements		23,421
March 2011 Warrants
Fair Value Inputs Liabilities Quantitative Information [Line Items]
Financial liabilities subject to fair value measurements	3,961	12,101
March 2011 Warrants | Basis of Fair Value Measurements, Level 3
Fair Value Inputs Liabilities Quantitative Information [Line Items]
Financial liabilities subject to fair value measurements	3,961	12,101
October 2009 Warrants
Fair Value Inputs Liabilities Quantitative Information [Line Items]
Financial liabilities subject to fair value measurements		11,320
October 2009 Warrants | Basis of Fair Value Measurements, Level 3
Fair Value Inputs Liabilities Quantitative Information [Line Items]
Financial liabilities subject to fair value measurements		$ 11,320