Derivative Instruments - Components of Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Derivative Instruments	$ 16,774	$ 15,509
Amended and Restated Convertible Notes [Member]
Derivative [Line Items]
Derivative Instruments	10,586	10,371
Amended and Restated Reimbursement Notes [Member]
Derivative [Line Items]
Derivative Instruments	1	7
Amended and Restated Bridge Notes [Member]
Derivative [Line Items]
Derivative Instruments	1,066	960
August 2009 Warrants [Member]
Derivative [Line Items]
Derivative instruments	765	597
June 2010 MHR Warrants [Member]
Derivative [Line Items]
Derivative instruments	260	249
Amended and Restated August 2010 Warrants [Member]
Derivative [Line Items]
Derivative instruments	538	420
August 2010 Investor Warrants [Member]
Derivative [Line Items]
Derivative instruments	148	171
August 2010 MHR Waiver Warrants [Member]
Derivative [Line Items]
Derivative instruments	200	156
July 2011 MHR Warrants [Member]
Derivative [Line Items]
Derivative instruments	618	482
July 2011 Warrants [Member]
Derivative [Line Items]
Derivative instruments	377	369
Amended and Restated July 2011 Warrants [Member]
Derivative [Line Items]
Derivative instruments	163	127
2013 MHR Modification Warrants [Member]
Derivative [Line Items]
Derivative instruments	$ 2,052	$ 1,600