Embedded Derivatives - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended								6 Months Ended
	Dec. 11, 2015	Jun. 30, 2016	Apr. 30, 2016	Dec. 31, 2015	May 31, 2015	Feb. 28, 2015	Aug. 31, 2014	Dec. 31, 2013	Jul. 31, 2012	Jun. 30, 2016	Jun. 30, 2015	May 31, 2016	Apr. 01, 2016
Derivative [Line Items]
Additional purchase of common stock shares										62,783,587
Derivative warrant liability fair value		$ 6,150		$ 10,493						$ 6,150
Proceeds from the exercise of warrants										$ 10,856	$ 10,151
Shares warrants outstanding		15,076,495								15,076,495
Series A
Derivative [Line Items]
Additional purchase of common stock shares						2,216,667				2,216,667
Shares warrants outstanding		228,332								228,332
Warrant , exercise price		$ 0.30								$ 0.30
Series B
Derivative [Line Items]
Additional purchase of common stock shares						2,216,667				2,216,667
Warrant , exercise price		$ 0.01								$ 0.01
Series C
Derivative [Line Items]
Additional purchase of common stock shares					430,000					430,000
Shares warrants outstanding		430,000								430,000
Warrant , exercise price		$ 1.84								$ 1.84
Series D
Derivative [Line Items]
Additional purchase of common stock shares				10,050,000						10,050,000
Shares warrants outstanding		43,600								43,600
Warrant , exercise price		$ 0.10								$ 0.10
Series E
Derivative [Line Items]
Additional purchase of common stock shares				8,000,000						8,000,000
Warrant , exercise price		$ 0.01								$ 0.01
Series F
Derivative [Line Items]
Additional purchase of common stock shares			10,292,858							10,292,858
Number of securities called by each warrant			1
Shares warrants outstanding		10,292,858								10,292,858
Warrant , exercise price		$ 0.30								$ 0.30
Series H
Derivative [Line Items]
Additional purchase of common stock shares			20,585,716							20,585,716
Number of securities called by each warrant			1
Shares warrants outstanding		2,577,000								2,577,000
Warrant , exercise price		$ 0.75								$ 0.75
Series G
Derivative [Line Items]
Additional purchase of common stock shares			6,571,429							6,571,429
Number of securities called by each warrant			1
Warrant , exercise price		$ 0.01								$ 0.01
Series A, D, E, G and H
Derivative [Line Items]
Common Stock Units Issued										42,782,210
Proceeds from the exercise of warrants										$ 10,900
7.5 Million Outstanding Series H
Derivative [Line Items]
Shares warrants outstanding												7,500,000
Warrant , exercise price			$ 0.75									$ 0.30
3 Million Outstanding Series H
Derivative [Line Items]
Shares warrants outstanding		3,000,000								3,000,000
Warrant , exercise price		$ 0.42								$ 0.42			$ 0.75
2 Million Outstanding Series H
Derivative [Line Items]
Shares warrants outstanding		2,000,000								2,000,000
Warrant , exercise price		$ 0.52								$ 0.52			$ 0.75
1 Million Outstanding Series H
Derivative [Line Items]
Shares warrants outstanding		1,000,000								1,000,000
Warrant , exercise price		$ 0.52								$ 0.52
Series D Warrant Agreement Amendment
Derivative [Line Items]
Shares warrants outstanding		4,167,391								4,167,391
Warrant , exercise price	$ 0.10	$ 0.175								$ 0.175
Warrants, exercise date	Jun. 11, 2016	Jun. 08, 2016
2013 Warrants
Derivative [Line Items]
Additional purchase of common stock shares								1,420,250		1,420,250
Shares warrants outstanding		1,115,476								1,115,476
Warrant , exercise price		$ 3.57								$ 3.57
2014 Warrants
Derivative [Line Items]
Additional purchase of common stock shares							1,000,000			1,000,000
Shares warrants outstanding		389,229								389,229
Warrant , exercise price		$ 2.51								$ 2.51
July 2022 Notes
Derivative [Line Items]
Percentage of convertible senior notes embedded derivatives									7.50%
7.5% convertible senior notes, maturity date									2022
2022 notes, conversion date									Jul. 01, 2017