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Stock-based Compensation - Summary of Company's Performance-based Restricted Stock Activity and Related Information (Detail) - Performance-Based Restricted Stock Units [Member] - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Shares, Unvested at beginning of period 0  
Shares, Granted 186,000 0
Shares, Vested 0  
Shares, Forfeited (109,550)  
Shares, Unvested at ending of period 76,450 0