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Stock Award Plans and Stock-based Compensation - Schedule of Grant Date Fair Value Per Share (Detail) - $ / shares
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2018
Jun. 30, 2017
Option Indexed to Issuer's Equity [Line Items]      
Number of options granted 30,500 237,000 69,600
Volatility 60.45% 60.45% 80.00%
Risk-free interest rate 2.94% 2.94% 0.58%
Weighted-average fair value per share of grants $ 2.08 $ 2.14 $ 1.05
Minimum [Member]      
Option Indexed to Issuer's Equity [Line Items]      
Weighted-average expected option term (in years) 6 years 3 months 6 years 3 months 5 years 6 months
Maximum [Member]      
Option Indexed to Issuer's Equity [Line Items]      
Weighted-average expected option term (in years) 9 years 11 months 19 days 9 years 11 months 19 days 6 years 3 months