Reconciliation of Numerator and Denominator Used in Computation of Basic and Diluted Net Income Loss Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Net loss	$ (1,716)	$ (3,460)	$ (1,907)	$ (8,834)	$ (7,735)	$ 2,260	$ (6,409)	$ (5,098)	$ (15,917)	$ (16,982)	$ (16,911)
Effect of revaluation of warrant liability									(2,059)	0	0
Adjusted net loss used for dilution calculation									$ (17,976)	$ (16,982)	$ (16,911)
Denominator
Basic weighted average number of common shares outstanding									54,515	48,050	40,300
Effect of dilutive potential common shares resulting from warrants accounted for as liabilities									546	0	0
Diluted weighted average number of common shares outstanding									55,061	48,050	40,300
Basic	$ (0.03)	$ (0.06)	$ (0.04)	$ (0.17)	$ (0.16)	$ 0.05	$ (0.13)	$ (0.11)	$ (0.29)	$ (0.35)	$ (0.42)
Diluted	$ (0.07)	$ (0.08)	$ (0.10)	$ (0.17)	$ (0.16)	$ 0.05	$ (0.13)	$ (0.11)	$ (0.33)	$ (0.35)	$ (0.42)