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Income taxes - Additional Information (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Income Tax Disclosure [Abstract]        
Income tax expense (benefit) $ 733,000 $ 2,512,000 $ (1,101,000) $ (231,000)
Effective income tax rate (199.82%) 19.60% 12.17% 3.50%
Annual effective income tax rate excluding discrete items     26.80% 23.35%
Effective income tax rate reconciliation result of removal deferred tax asset amount $ 0   $ 483,000  
Effective income tax rate reconciliation due to vesting of stock-based compensation awards and change in stock price amount 853,000   853,000  
Deferred tax assets tax holiday 784,000   784,000  
Penalties or interest recorded $ 0   $ 0