Net Loss Per Common Share - Reconciliation of Numerator and Denominator (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator:
Net loss - basic	$ (8,306)	$ (766)	$ (19,460)	$ (7,875)
Less: noncash income from change in fair value of common stock warrants	(308)	(6,665)		(8,122)
Net loss - diluted	$ (8,614)	$ (7,431)	$ (19,460)	$ (15,997)
Denominator:
Weighted average common shares outstanding	71,334	59,347	69,046	59,325
Dilutive effect of warrants	1,481	3,651		4,108
Weighted-average common shares outstanding and dilutive potential common shares — diluted	72,815	62,998	69,046	63,433
Net loss per share
Basic	$ (0.12)	$ (0.01)	$ (0.28)	$ (0.13)
Diluted	$ (0.12)	$ (0.12)	$ (0.28)	$ (0.25)