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Stock-Based Compensation - Restricted Stock Units Activity (Detail) - Outstanding Restricted Stock Units
3 Months Ended
Mar. 31, 2018
$ / shares
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Number of Shares, Unvested, Beginning balance | shares 888,189
Number of Shares, Granted | shares 139,300
Number of Shares, Vested | shares (70,200)
Number of Shares, Forfeited | shares (83,125)
Number of Shares, Unvested, Ending balance | shares 874,164
Weighted-Average Grant Date Fair Value, Unvested, beginning balance | $ / shares $ 8.14
Weighted-Average Grant Date Fair Value, Granted | $ / shares 3.74
Weighted-Average Grant Date Fair Value, Vested | $ / shares 6.31
Weighted-Average Grant Date Fair Value, Forfeited | $ / shares 8.13
Weighted-Average Grant Date Fair Value, Unvested, ending balance | $ / shares $ 7.58