Quarterly report pursuant to Section 13 or 15(d)

Summary of Unvested Stock Option Activity (Detail)

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Summary of Unvested Stock Option Activity (Detail) - $ / shares
shares in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Weighted Average Grant Date Fair Value        
Granted $ 1.27 $ 3.94 $ 1.46 $ 4.60
Stock Options        
Shares        
Beginning Balance     846  
Granted     402  
Vested     (240)  
Forfeited or cancelled     (99)  
Ending Balance 909   909  
Weighted Average Grant Date Fair Value        
Beginning Balance     $ 3.14  
Granted     1.46  
Vested     3.59  
Forfeited or cancelled     2.55  
Ending Balance $ 2.34   $ 2.34