Derivative Instruments - Components of Derivative Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative instruments	$ 47,966	$ 29,920
Convertible Notes [Member]
Derivative [Line Items]
Derivative instruments	30,823	21,501
Reimbursement Notes [Member]
Derivative [Line Items]
Derivative instruments	1,118	705
Bridge Notes [Member]
Derivative [Line Items]
Derivative instruments	3,130	1,926
Amended and Restated August 2009 Warrants [Member]
Derivative [Line Items]
Derivative instruments	2,142	930
Amended and Restated June 2010 MHR Warrants [Member]
Derivative [Line Items]
Derivative instruments	552	282
Amended and Restated August 2010 Warrants [Member]
Derivative [Line Items]
Derivative instruments	1,507	654
August 2010 Investor Warrants [Member]
Derivative [Line Items]
Derivative instruments		29
Amended and Restated August 2010 MHR Waiver Warrants [Member]
Derivative [Line Items]
Derivative instruments	560	243
Amended and Restated July 2011 Warrants [Member]
Derivative [Line Items]
Derivative instruments	1,729	750
July 2011 Investor Warrants [Member]
Derivative [Line Items]
Derivative instruments	205	210
Amended and Restated July 2011 MHR Waiver Warrants [Member]
Derivative [Line Items]
Derivative instruments	456	198
May 2013 MHR Modification Warrants [Member]
Derivative [Line Items]
Derivative instruments	$ 5,744	$ 2,492