Net Loss Per Common Share - Reconciliation of Numerator and Denominator (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Numerator:    
Net loss - basic $ (11,154) $ (7,109)
Less: noncash income from change in fair value of common stock warrants   1,757
Net loss - diluted $ (11,154) $ (8,866)
Denominator:    
Weighted average common shares outstanding 66,732 59,303
Dilutive effect of warrants 0 1,997
Weighted-average common shares outstanding and dilutive potential common shares — diluted 66,732 61,300
Net loss per share    
Basic $ (0.17) $ (0.12)
Diluted $ (0.17) $ (0.14)