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Stock and Stock-based Compensation - Summary of Unvested Restricted Stock Units (Detail) - Restricted Stock Units (RSUs) - $ / shares
1 Months Ended 12 Months Ended
Feb. 28, 2017
Dec. 31, 2017
Dec. 31, 2016
Summary of unvested restricted stock units      
Unvested restricted stock units, Beginning Balance   218,412 315,847
Granted restricted stock unit 605,000 56,759 31,327
Vested   (112,340) (105,443)
Forfeited   (2,289) (23,319)
Unvested restricted stock units, Ending Balance   165,120 218,412
Weighted Average Fair Value Per RSU, Beginning Balance   $ 4.28 $ 3.99
Awarded   1.48 2.81
Vested   3.99 4.66
Forfeited   4.41 5.12
Weighted Average Fair Value Per RSU, Ending Balance   $ 3.40 $ 4.28