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Common Stock and Warrants - Fair Value of Warrants Estimated Using Black-Scholes Option Pricing Model with Weighted Average Assumptions (Detail)
3 Months Ended
Dec. 29, 2017
$ / shares
Dec. 28, 2017
$ / shares
Dec. 22, 2017
$ / shares
Mar. 31, 2018
$ / shares
Mar. 31, 2017
$ / shares
Mar. 31, 2018
$ / shares
Warrants Granted            
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]            
Stock price           $ 5.45
Exercise price           $ 7.50
Warrant term       3 years    
Expected volatility       83.83%    
Risk-free interest rate       0.60%    
Dividend rate       0.00%    
Warrants Granted | December 2017 Financing            
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]            
Stock price $ 12.32 $ 12.45 $ 10.60      
Exercise price $ 12.25 $ 12.25 $ 12.25      
Warrant term 3 years 3 years 3 years      
Expected volatility 60.24% 60.24% 60.24%      
Risk-free interest rate 1.98% 2.00% 2.01%      
Dividend rate 0.00% 0.00% 0.00%      
Warrants Outstanding            
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]            
Stock price       $ 10.11 $ 7.80  
Exercise price       $ 12.72 $ 8.10  
Warrant term       2 years 3 months 14 days 1 year 7 months 24 days  
Expected volatility       63.77% 94.21%  
Risk-free interest rate       2.26% 0.75%  
Dividend rate       0.00% 0.00%