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Stockholders' Equity - Incentive Plans (Detail) - USD ($)
12 Months Ended
Jan. 01, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
2003 Stock Incentive Plan        
Incentive plans        
Period from date of termination that any vested options shall expire   60 days    
Expiration period   10 years    
Intrinsic value of options exercised   $ 716,920 $ 103,638 $ 97,707
Cash proceeds from exercise of stock options   $ 59,659 $ 27,357 $ 44,771
Options exercised   46,131 16,608 28,368
Fair value of shares vested     $ 1,573 $ 16,024
2003 Stock Incentive Plan | Upon first anniversary of start date        
Incentive plans        
Percent of shares subject to option grant that will vest   25.00%    
2003 Stock Incentive Plan | Each month after the first anniversary        
Incentive plans        
Percent of shares subject to option grant that will vest   2.083%    
2013 Equity Incentive Plan        
Incentive plans        
Period from date of termination that any vested options shall expire   90 days    
Expiration period   10 years    
Unrecognized compensation expense related to unvested options   $ 9,129,271    
Period for unrecognized compensation expense related to unvested options yet has not been recognized   2 years 8 months 12 days    
Intrinsic value of options exercised   $ 1,344,026 385,701 2,275
Cash proceeds from exercise of stock options   $ 962,530 $ 346,019 $ 27,825
Options exercised   144,182 54,521 3,500
Fair value of shares vested   $ 3,003,632 $ 3,506,568 $ 3,053,086
2013 Equity Incentive Plan | Upon first anniversary of start date        
Incentive plans        
Percent of shares subject to option grant that will vest   25.00%    
2013 Equity Incentive Plan | Each month after the first anniversary        
Incentive plans        
Percent of shares subject to option grant that will vest   2.083%    
Common Stock        
Incentive plans        
Options exercised     71,129  
Common Stock | 2013 Equity Incentive Plan        
Authorized shares        
Common stock authorized under 2013 plan 5,162,816      
Automatic increase in number of shares reserved for issuance as a percentage of the total common stock outstanding at the end of the prior year 3.00% 3.00%    
Maximum number of shares that may be issued pursuant to exercise of incentive stock   20,000,000    
Increase in number of shares of common stock 1,294,822      
Common Stock | 2013 Equity Incentive Plan | Maximum        
Authorized shares        
Common stock authorized under 2013 plan   1,000,000