Quarterly report pursuant to Section 13 or 15(d)

Summary of Option Activity (Detail)

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Summary of Option Activity (Detail) - 2002 Stock Incentive Plan - $ / shares
shares in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Shares    
Beginning Balance 6,737  
Granted at fair market value 2,519  
Exercised (6)  
Forfeited, cancelled, or expired (471)  
Ending Balance 8,779 6,737
Options exercisable at March 31, 2018 4,264  
Vested options expired during the quarter ended March 31, 2018 920  
Weighted Average Exercise Price    
Beginning Balance $ 1.80  
Granted at fair market value 0.42  
Exercised 0.42  
Forfeited, cancelled, or expired 3.58  
Ending Balance 1.40 $ 1.80
Options exercisable at March 31, 2018 1.88  
Vested options expired during the quarter ended March 31, 2018 $ 2.79  
Weighted Average Remaining Contractual Term (Years)    
Options outstanding 7 years 5 months 4 days 7 years 2 months 15 days
Options exercisable 5 years 7 months 13 days