Reconciliation of Numerator and Denominator Used in Computation of Basic and Diluted Net Income Loss per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator for Basic and Diluted:
Net loss used for basic calculation	$ (14,756)	$ (15,680)	$ (15,972)	$ (9,460)	$ (20,182)	$ (10,759)	$ (7,589)	$ (225)	$ (55,868)	$ (38,755)	$ (43,337)
Effect of revaluation of warrant liability									(3,566)	(7,708)
Adjusted net loss used for dilution calculation									$ (59,434)	$ (46,463)	$ (43,337)
Denominator:
Basic weighted average number of shares outstanding									96,068	74,767	67,569
Effect of dilutive potential shares									837	1,767
Diluted weighted average number of shares outstanding									96,905	76,534	67,569
Net loss per share:
Basic	$ (0.15)	$ (0.16)	$ (0.17)	$ (0.10)	$ (0.26)	$ (0.14)	$ (0.10)	$ 0.00	$ (0.58)	$ (0.52)	$ (0.64)
Diluted	$ (0.15)	$ (0.17)	$ (0.17)	$ (0.17)	$ (0.26)	$ (0.16)	$ (0.16)	$ (0.12)	$ (0.61)	$ (0.61)	$ (0.64)