Annual report pursuant to Section 13 and 15(d)

Common Stock, Stock-Based Awards and Warrants - Schedule of Restricted Stock Activity (Details)

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Common Stock, Stock-Based Awards and Warrants - Schedule of Restricted Stock Activity (Details) - Restricted stock units - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Units [Abstract]      
Beginning Balance (in shares) 4,697    
Granted (in shares) 3,392    
Vested (in shares) (1,325)    
Forfeited (in shares) (852)    
Ending Balance (in shares) 5,913 4,697  
Vested and expected to vest (in shares) 5,891    
Weighted Average Exercise Price (in dollars per share):      
Beginning Balance (in dollars per share) $ 3.53    
Granted (in dollars per share) 2.65    
Vested (in dollars per share) 3.61    
Forfeited (in dollars per share) 3.42    
Ending Balance (in dollars per share) 3.03 $ 3.53  
Vested and expected to vest (in dollars per share) $ 3.02    
Aggregate Intrinsic Value      
Balance $ 13,185 $ 10,757  
Vested and expected to vest 13,138    
Fair value of instruments vested in period $ 2,200 $ 1,200 $ 2,100