Annual report pursuant to Section 13 and 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
12 Months Ended
Feb. 06, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Shares        
Beginning Balance   358,000 84,000
Granted 16,000 2,836,000 470,000 181,000
Vested   (604,000) (81,000) (97,000)
Forfeited or cancelled   (427,000) (115,000)
Ending Balance   2,163,000 358,000 84,000