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Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended
Apr. 30, 2016
Mar. 31, 2019
Mar. 31, 2018
Accounting Policies [Abstract]      
Accounts receivable written off   $ 0  
One-time contingent regulatory milestone payment pursuant to agreement with Ipsen Group $ 8,000,000    
Finite-lived intangible assets, net $ 8,000,000    
Amortization of intangible assets   370,000 $ 369,000
Estimated future amortization expense, remainder of 2019   1,100,000  
Estimated future amortization expense, 2020   1,500,000  
Estimated future amortization expense, 2021   $ 1,000,000