Change in Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Beginning Balance	$ 69,431	$ 123,125
Loss (gain) on change in fair value of derivative liabilities	(47,710)	35,344	22,669
Initial measurement-December 2012 financing		14,600
Transfers to equity	(24)	(103,885)
Ending Balance	17,994	69,431	123,125
Derivative Instrument
Derivatives, Fair Value [Line Items]
Loss (gain) on change in fair value of derivative liabilities	(47,710)	35,344
Warrant
Derivatives, Fair Value [Line Items]
Compensation expense (income) for change in fair value of warrants issued to former employees	(3,703)	247	(96)
Warrants Issued October 2009
Derivatives, Fair Value [Line Items]
Beginning Balance	54,854	123,125
Transfers to equity	(24)	(103,885)
Ending Balance	6,894	54,854
Warrants Issued October 2009 | Derivative Instrument
Derivatives, Fair Value [Line Items]
Loss (gain) on change in fair value of derivative liabilities	(44,233)	35,367
Warrants Issued October 2009 | Warrant
Derivatives, Fair Value [Line Items]
Compensation expense (income) for change in fair value of warrants issued to former employees	(3,703)	247
Embedded Derivative Financial Instruments
Derivatives, Fair Value [Line Items]
Beginning Balance	14,577
Loss (gain) on change in fair value of derivative liabilities	(3,500)	(20)
Initial measurement-December 2012 financing		14,600
Ending Balance	11,100	14,577
Embedded Derivative Financial Instruments | Derivative Instrument
Derivatives, Fair Value [Line Items]
Loss (gain) on change in fair value of derivative liabilities	$ (3,477)	$ (23)