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Stock-Based Compensation - Summary of Restricted Stock Activity (Detail) - 2012 Equity Incentive Plan - Restricted Stock - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Number of Shares Unvested, Beginning balance 274,000 290,000  
Number of Shares, Granted 352,000 161,000 44,000
Number of Shares, Vested (90,000) (167,000)  
Number of Shares, Forfeitures (2,000) (10,000)  
Number of Shares Unvested, Ending balance 534,000 274,000 290,000
Weighted Average Unvested, Beginning balance $ 7.35 $ 8.02  
Weighted Average, Granted 14.77 3.85  
Weighted Average, Vested 8.01 6.79  
Weighted Average, Forfeitures 8.91 6.00  
Weighted Average Unvested, Ending balance $ 11.27 $ 7.35 $ 8.02