Quarterly report pursuant to Section 13 or 15(d)

Summary of Warrant Activity (Detail)

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Summary of Warrant Activity (Detail) - Warrants
shares in Thousands
 3 Months Ended
Mar. 31, 2018
$ / shares
shares
Shares  
Beginning Balance | shares 6,126
Granted or Issued | shares 258
Ending Balance | shares 6,384
Warrants exercisable at March 31, 2018 | shares 6,249
Weighted Average Exercise Price  
Beginning Balance | $ / shares $ 1.93
Granted or Issued | $ / shares 0.47
Ending Balance | $ / shares 1.87
Warrants exercisable at March 31, 2018 | $ / shares $ 1.82