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Stock and Stock-based Compensation - Summary of Unvested Restricted Stock Units (Detail) - Restricted Stock Units (RSUs) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Summary of unvested restricted stock units    
Unvested restricted stock units, Beginning Balance 165,120 218,412
Granted restricted stock unit 91,000 56,759
Vested (154,874) (112,340)
Forfeited (96,215) (2,289)
Unvested restricted stock units, Ending Balance 5,031 165,120
Weighted Average Fair Value Per RSU, Beginning Balance $ 3.40 $ 4.28
Awarded 1.35 1.48
Vested 2.87 3.99
Forfeited 2.51 4.41
Weighted Average Fair Value Per RSU, Ending Balance $ 2.92 $ 3.40