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Summary of Significant Accounting Policies - Additional Information (Detail)
 1 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2013
USD ($)
Mar. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2011
USD ($)
Dec. 31, 2010
USD ($)
Tranche
Apr. 03, 2018
$ / shares
shares
Summary Of Significant Accounting Policies [Line Items]            
Stock forward-split ratio   6.6841954        
Capital stock shares authorized | shares   210,000,000        
Common stock, shares authorized | shares   200,000,000 200,000,000     200,000,000
Common stock, par value | $ / shares   $ 0.001 $ 0.001     $ 0.001
Preferred stock shares authorized | shares   10,000,000        
Preferred stock, par value | $ / shares   $ 0.001        
Preferred stock share outstanding | shares   0        
Cash equivalents   $ 0 $ 0      
Cash, uninsured amount   6,695,367 8,465,768      
Cash, FDIC insured amount   250,000 250,000      
Debt instrument, face amount   4,500,000        
Change in fair value of investment unit $ 2,500,000 0        
Impairments of our long-lived assets   $ 0 $ 0      
State of Texas Emerging Fund ("TETF")            
Summary Of Significant Accounting Policies [Line Items]            
Debt instrument, face amount         $ 4,500,000  
Number of tranches | Tranche         2  
Proceeds from other debt       $ 2,250,000 $ 2,250,000  
U.S. Treasury Department            
Summary Of Significant Accounting Policies [Line Items]            
Proceeds from award         $ 244,500  
Minimum            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, useful life   3 years        
Maximum            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, useful life   5 years