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Convertible Notes - Summary of the carrying value of the convertible notes (Detail) - USD ($)
$ in Thousands
Sep. 30, 2020
Dec. 31, 2019
Debt Instrument [Line Items]    
Carrying amount   $ 175,956
Convertible Senior Notes Due Two Thousand And Twenty Three [Member]    
Debt Instrument [Line Items]    
Principal amount $ 175,000  
Plus: premium on Additional Notes 250  
Carrying amount 175,250  
Less: Unamortized debt discount and issuance costs [1] (9,431)  
Carrying amount $ 165,819  
Effective interest rate [2] 6.29%  
Convertible Senior Notes Due Two Thousand And Twenty Three [Member] | Additional Notes [Member]    
Debt Instrument [Line Items]    
Principal amount $ 25,000  
Plus: premium on Additional Notes 250  
Carrying amount 25,250  
Less: Unamortized debt discount and issuance costs [1] (1,613)  
Carrying amount $ 23,637  
Effective interest rate [2] 6.37%  
Convertible Senior Notes Due Two Thousand And Twenty Three [Member] | Existing Notes [Member]    
Debt Instrument [Line Items]    
Principal amount $ 150,000  
Carrying amount 150,000  
Less: Unamortized debt discount and issuance costs [1] (7,818)  
Carrying amount $ 142,182  
Effective interest rate [2] 6.28%  
[1] The debt discount arose from the bifurcation of the conversion option. The unamortized debt discount and issuance costs is reported net of the unamortized premium on the Additional Notes.
[2] Includes amortization of the discount arising from the bifurcation of the conversion option, amortization of the issuance costs allocated to the Convertible Notes and amortization of the premium associated with the Additional Notes.