Quarterly report pursuant to Section 13 or 15(d)

Summary of Unvested Restricted Stock Units (Detail)

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Summary of Unvested Restricted Stock Units (Detail) - Restricted Stock Units (RSUs)
shares in Thousands
6 Months Ended
Jun. 30, 2018
$ / shares
shares
Shares  
Beginning Balance | shares 358
Granted | shares 2,456
Vested | shares (212)
Forfeited or cancelled | shares (208)
Ending Balance | shares 2,394
Weighted Average Grant Date Fair Value  
Beginning Balance | $ / shares $ 4.84
Granted | $ / shares 1.44
Vested | $ / shares 2.38
Forfeited or cancelled | $ / shares 4.48
Ending Balance | $ / shares $ 1.51