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Fair Value Measurements - Additional Information (Detail) - CRG [Member] - Term Loan Agreement [Member] - USD ($)
1 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Additional interest rate, event of default (as a percent)   4.00%    
Line of credit, additional borrowing capacity       $ 10,000,000
Debt instrument covenant compliance revenue targeted for fiscal year $ 9,000,000   $ 7,000,000  
Derivative liability $ 2,200,000 $ 2,200,000 $ 2,100,000  
Contingent Interest Beginning in 2020 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Contingent payment of interest rate   4.00%    
Contingent Interest Beginning in 2020 [Member] | Measurement Input, Discount Rate [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Estimated fair value of discount rate   70.00%    
Contingent Interest Beginning in 2021        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Contingent payment of interest rate   4.00%    
Contingent Interest Beginning in 2021 | Measurement Input, Discount Rate [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Estimated fair value of discount rate   30.00%